How to book US antigen test for return flight

[Greentime101]

Am I being a total banana? Im flying to the US next month.

Booked test required to get me there ✅
Aware of the 2 day test needed on return ✅

Can’t find info on the test I need to book to get me back on the flight home. If I try and search/book anything in the US it recognises I am in the UK & I cannot access?

There are pop up tents all over, particularly close to Time Square. My research says you need to go early as they are busy.