Here's another one -- Search your phone for the ringtone you want to assign to a contact. Tap and hold on that ringtone until a pop-up window appears with some options. Choose Set as > Caller ringtone > choose contact > Save.
How about trying this one -- To add a ringtone to a specific contact, select a Contact > Options > Options > Ringtone. I got this info from a LG representative. Hopefully you get it right this time.
no option for Contact (choose) > Menu > Edit > Assign Ringtone