Open PGM-Win software with a configuration that contains a TEL-14 interface card, in the configuration menu look for the DTMF tab and click on it.
•  On the lefthand side of screen highlight the desired TEL-14 interface.  
•  The check boxes above allow one or two digit codes, multiple codes, first code only and access prompts
•  Select the desired TEL-14 interface from the lefthand side and double click on it to open up the available interfaces, panels etc that you want to assign codes to
   (work screen background is now white on the Talk 1, 2, 3 and Listen entry boxes)
•  Highlight an item and with your mouse go over to the center of the screen and assign the highlighted item to a one or two digit code
•  When done click on the Apply button to download to frame
 Now with telephone dial the phone # associated with the TEL-14 interface, you should hear an access prompt when the line connects, using telephone keypad dial the one or two digit code and you should now be connected to the panel / interface / partyline / fixed group.
For added security you can assign a 4 digit code in the Setup / System Preferences menu.  After dialing in enter the 4 digit code and wait for the access prompt before entering the one or two digit code.
A PDF is attached below with screen shots from PGM-Win software.