usa – Confused on UK to US travel in regards to testing

Traveling from UK to USA on 13th September with a layover in Amsterdam.

On the way back it’s USA to UK with a layover in Amsterdam.

Traveling with my US wife (I’m a British citizen). Both fully vaccinated.

As far as I can tell, we need a negative viral test to fly to USA (and to complete the negative attestation form) and that’s it.

However on the way back to enter UK, we’ll need a pre departure test, then another test on day 2 and to complete the passenger locator form.

I’m very confused on where to book all these tests since the CDC website just says an antigen test is sufficient (but how do I prove the result, over text?) And the UK government website has no information on where to complete a test in the USA before we fly back.

I would appreciate some help since it’s bugging me out if somebody who has traveled from UK to USA in recent weeks could chip in.

Thanks all!