Hi:) 

i am really new to interrail and really excited about it. However i have a small problem.

so i booked a reservation a few weeks ago from Amsterdam Centraal to London. However, my plans have slightly changed and at the date of this journey I am in Bruxelles instead of in Amsterdam. Is it possible to board the train (where I have a seat reservation from Amsterdam to London) also from Bruxelles (which is two stops after Amsterdam)? Or will the reservation not be valid if you do not board the train at the station of your reservation?

thankss if anyone has the answer to my question:) have a lovely evening🥰

Please ask indeed Eurostar. The problem is that you have to go through a check in and immigration process already before getting on the Eurostar and iam not sure if you can just go through the process in Brussels when you first booked from Amsterdam.