You need to assign it from ext. 10 or 11. You will need to find out what line number it is in the system before beginning (line 1, line 2, etc). You can do that by pressing Feature 00 on your phone, then pressing the button that the line appears on. It should then say "Immediate ring L04" (or L05 or whatever depending upon the line number) in the display. Once you have this information, you have to program the actual feature from extension 10 or 11. From ext. 10/11, you would press the Feature key, then 00 on the keypad. The Left Intercom Button Twice, then #209. The display will then prompt you for the line number. Line 1 is 01, line 2 is 02, etc. You can then Press 1-8 to hear the different ring patterns available for that line. when you hear one you like, just press Feature 00 again and that will take you back out of programming mode.