"To know the exact amount to recharge with to be eligible for this offer -Subscribers can go to mytatasky.com or login to the Tata Sky mobile app and proceed with the recharge. In case they are not sure of the correct amount, they can simply enter a smaller amount, e.g. Rs100 and proceed further. Eligible subscribers will be shown a pop-up with the correct amount required for the annual / semi-annual recharge. Subscribers can then choose the correct amount, proceed further and choose a ICICI bank Credit/Debit card for completing the transaction."
To recharge or to find the amount for 12 months / 6 months follow the above Rs.100 method.
If you want different amount to recharge you can modify your pack then recharge twelve or six months of that.