1. First copy this link - https://www.airtel.in/myaccount/NavigationApp?num=MobileNumber
and replace "MobileNumber" with your 10 digit Airtel mobile number.
2. Open that link.
3. Login to it using your airtel account if you already have or get an OTP code to your mobile to log in.
4. In that page click on Do More (below recharge option) & then click Transaction details...
5. Now a page opens with address - https://www.airtel.in ....... msisdn=XXXXXXXXXXXXXXXX
where XXXXXXXXXXXXXXXX is your MSIDN code...Copy that MSIDN CODE....
6. Now paste that code to this link replacing XXXXXXXXXXXXXXXX with your MSIDN CODE - https://www.airtel.in/account/3gDongle/quickLink.jsp?msisdn=XXXXXXXXXXXXXXXX
7. Now open this link and click on the offer image.
8. Now enter any alternate mobile number and email id.
9. Now you will receive a code to that alternate mobile number.
10. Enter that code and you will get your offer activated.