You mention that you have your letter of validation, but it is also worth setting up your account on the FAA IACRA website, as your license will be processed and issued from there.
Nowadays the FAA (some regions yes and some regions no) are moving away from the booked visit to the regional FAA office, and are sending out lists of FPE's (foreign pilot examiners) and you are free to make your own appointment with an FPE that lives close to you.