Login to your Xfinity Account
Claim the Xfinity Reward Offer for ‘Get Independence Day - on us’ offer for Free
make sure you claim the offer first before redeeming/purchasing
You may also claim it in the Xfinity App

In the Xfinity On Demand service, search Independence Day film in HD format
select the ‘Buy‘ offer
push play to watch
Your promotional offer will automatically be applied to the digital film
you will get the credit on your next bill cycle