1) Make sure that the current input is TV. Then press Menu on either the TV or the remote.
2) Press Ch+ or Ch- to highligh Setup then press OK.
3) Press Vol+/Vol- to highlight TV or CATV as needed for the channels you wish to add or erase.
4) Then use Ch+/Ch- to highlight Channel and then press Vol+/Vol- to enter the channel number that you want to add.
5) Press Ch+/Ch- repeatedly to highlight Add/Erase then use Vol+/Vol- to select whether to add or erase the channel selected above (step 4).
6) Press Menu repeatedly to exit the OSD (or wait until the OSD closes after a period with no key presses).
Then use the Ch+/Ch- buttons to scroll through the channels in memory to see the change.
The manual for your 24F512T is available here: http://support.ttetech.com/RCATV/Assets/pdfs/24F512T_1641309F_IB_e-06.pdf
. See page 13 of the manual for extra information on manual tuning and page 15 to add and remove channels from the channel list.
I hope this helps.