KX-TGA101S is an add-on handset for a Panasonic KX-TG1000 series cordless phone system. One of the models that is compatible with the handset is the KX-TG1032S. You can find the manual for the phone system on the product page here: https://shop.panasonic.com/support-only/KX-TG1032S.html
. Assuming that you do not have voice mail from your telephone provider, you can change the number of rings from the Answering Device Settings Menu.
Start with the phone system in standby (no incoming or outgoing calls) mode. Press Menu and use the up/down keys to navigate to Answering Device. Press OK to enter the sub-menu. Navigate to Settings and press OK. Navigate to Ring Count and press OK. Use the up/down arrows to choose a new number of rings. Press OK to save and press Off to exit the menu system. Note: if the ring count is set to Toll Saver mode, the answering system will pick up on the second ring if there are new messages. It will pick up the incoming call on the fourth ring if there are no new messages.
See page 31 of the manual for the KX-TG1032 for this information. See page 23 for the way to navigate through the menu and a list of the menu tree items. The current link to the manual is ftp://ftp.panasonic.com/telephone/om/kx-tg1031_en_om.pdf
I hope this helps.