Question about German railpass - where to validate

It is underneath Terminal 1 (downstairs). Follow the signs. If you arrive at Terminal 2, take the people mover between terminals to go over to Terminal 1.

The counter at FRA is in the Reisezentrum in the Regionalbahnhof, which, technically is under the building across the street from Terminal 1, but you get to it by going down stairs inside the outside wall from the arrival hall of Terminal 1, through a passage under the access road, and into the Bahnhof. However, if you are using a pass, you will likely be leaving FRA on an express train (ICE, IC, or EC). Those trains use the Fernbahnhof, and you can validate your railpass at the ticket counter in the top level of the Fernbahnhof. To get to the Fernbahnhof, go up the escalator to the second floor mezzanine of Terminal 1's arrival hall, and across the pedestrian bridge over the access road. Follow the hall through the building to the Fernbahnhof. When you enter the Fernbahnhof, which is a glass domed atrium, turn left to get to the ticket counter. To find the "people mover" from Terminal 2 to Terminal 1, follow the signs for the "Skyline". It goes from the roof of T2 to the roof of T1.

Thank you both! This really helps.