If you have carry on you can go straight to the next gate. If you have checked bags that have been checked all the way through to EIS by your airline you can go straight to the next gate. I believe you need to check in at the gate again. I assume this because they were telling people to make sure their boarding passes were marked to show the documents had been checked in SJU yesterday (Silver). If you have checked bags that have not been checked all the way through then you will need to collect them at baggage claim and check them in with the airline for your next flight. To do that you will have to leave the secure area but if you show your onward flight reservation to the Covid security people they will direct you to the elevator to the check in area. After that you check in for your next flight. There you will need to show passports, negative Covid test result, and vaccination card. Then you go through TSA security and head to the departure gates. TSA pre is very helpful to have, at least it was on en lines were long.