Look for the make of Airtel DTH box. It is normally on the backside of the box. Now look for remote for the box under "Satellite" category in the remote code list provided with AVR. The same can also be accessed in the disc provided with AVR, else you can download the same.
Activating procedure has been given in the AVR manual.
I had tried that. THe DTH box is made by Huawei. But the remote control codes doesn't have code for this make.