Setting the number of rings before answering machine kicks in

Likely the machine answer option is set to AUTO. This may be change to any number of rings from 2 - 9.

To set number of rings;

1. [MENU] #211
2. Select number of rings with up/down key.
3. [OK]
4. [OFF/PWR]

Download a copy of the manual for more detailed instruction from...

https://www.manualslib.com/manual/817662/Panasonic-Kx-Tg6821al.html

Answering system settings Number of rings before the unit answers calls You can change the number of times the phone rings "Ring count" before the unit answers calls. You can select 2 to 7 rings, or "Toll saver". The default setting is "4". "Toll saver": The unit's answering system answers at the end of the 2nd ring when new messages have been recorded, or at the end of the 4th ring when there are no new messages. If you call your phone from outside to listen to new messages , you will know that there are no new messages when the phone rings for the 3rd time. You can then hang up without being charged for the call. 1 {MENU} i {#}{2}{1}{1} 2 {V}/{^}: Select the desired setting. i {Save} i {OFF}

Press and hold the STOP/SET button for two seconds. After the time and day you can change the rings to answer.

Full details are in the "Changing the Settings" section in the third column of the manual. If you need a manual, you can download one at
http://www.home-electronics.net/USER-GUIDES/29888_DOM_EN_AN_IB.pdf

Probably a cordless right?If it is,there should be a function button on the handset.Without pressing to dial out,press or hold down the function button.If there is a directional type button,you may have to press down or keep pressing the function button to cycle through the options.Once you find the ring set,it will probably require the directional button up or down to change the number of rings.Function could also be on the base,but it's usually on the handset.You may have to play around with a couple other buttons if there is no directional button but most seem to have the directional button these days. Good luck!

your service provider will provide you with a code to alter the settings for the answer phone , you can adjust how long before the answer phone kicks in and whether the answer phone is on or off

Try typing the following into your phone, then hitting SEND - replace the words in brackets with the relevant numbers):
**61*(voicemail or diversion phone number)**(seconds delay before diverting)#

This works for "Divert on No Answer". To check the status of this diversion use *#61#

1. Press set button
2. Use next and previous buttons to select number of rings setting and press set.
3. Select the number of rings you want.
4. press set again to save setting.

I hope this helps. Here's the manual:
29869GE2 Digital Answering Machine

• The Rings to Answer feature might not be set to answer after the
appropriate number of rings for your office setup.
• If you have a voice mail service at the same phone number you use
for fax calls, you must receive faxes manually, not automatically. For
information on how to receive faxes manually, see receive a fax
manually from a phone on page 48.
• If you have a PC modem on the same phone line with your
HP Officejet, check to make sure that the modem’s software is not
set to receive faxes automatically. Modems with this auto fax
receive feature turned on will take over the phone line to receive all
incoming faxes, which will prevent the HP Officejet from receiving
fax calls.
• If you have an answering machine on the same phone line with
your HP Officejet, you might have one of the following problems:
– Your outgoing message might be too long or too loud to allow
the HP Officejet to detect fax tones, and the calling fax machine
might disconnect.
– Your answering machine might not have enough quiet time after
your outgoing message to allow the HP Officejet to detect fax
tones. This problem is more common with digital answering
machines.
The following actions might help solve these problems:
a. Disconnect the answering machine and then try receiving a fax.
If faxing is successful without it, the answering machine might
be causing the problem.
b. Reconnect the answering machine and re-record your outgoing
message. Make sure the message is as short as possible (no
more than 10 seconds long), and that you speak softly and
slowly when recording it. Try again to receive a fax.
• If you have a special ring pattern for your fax phone number (using
a distinctive ring service through your telephone company), make
sure that the Answer Ring Pattern feature on your HP Officejet is set
to match. For example, if the phone company has assigned your
fax number a double ring pattern, make sure Double Rings is
selected as the Answer Ring Pattern setting. For information on
changing this setting, see change the answer ring pattern
(distinctive ringing) on page 63.
Note that some ring patterns cannot be recognized by the
HP Officejet, such as those with alternating short and long ringing
patterns. If you are having problems with a ring pattern of this type,
ask your phone company to assign a non-alternating ring pattern.

http://h10032.www1.hp.com/ctg/Manual/c00095626.pdf

I can't seem to get the security code entered.  It won't change.  None of the numbers will change when I try to set it up.

Press the 'Change' button
Press the 'Setup' button until you hear the voice say "Number of rings"
Then use the "Skip" and "Repeat" buttons to change the number.
Press the "Change" button to finish.