Log into your account and go to the top tab that says special deals and offers then go to cashback offers. There will likely be several different ones and you have to activate them to get them and they all have expiration dates. I currently have one that is good for Hampton inn and Hilton garden inn this month and I had one for most other Hiltons that just expired.

After you activate the offers, you just use the card and it takes a month or so but the cashback is credited back to your account.

The offers don't seem to come on the business version just the personal.

It is when you pay that counts by the way, I have booked prepaid rates before expiration and stayed after and I got the cash back.