I'm guessing it's not a Canadian license. You will need to:
1. Pass a TSA background check
2. Complete the ATP Certificate Training Program
3. Pass the ATM written test
4. Pass an ATP checkride
If the 777 training was conducted under a Part 142 program you have 60 days from the completion of the training to pass the checkride. If you can't do all the above in 60 days and you want the 777 type on your certificate you will have to complete a 777 training program conducted under 142 and pass a checkride. If you just want a generic ATP MEL you just need to pass a checkride in a light twin. But you would then need at least a FAA third class medical.