Eurostars are awfully simple to board on a wheelchair. If a platform hasn't been already provided (as it should be if you booked online) you merely need to as

Eurostars are awfully simple to board on a wheelchair. If a platform hasn't been already provided (as it should be if you booked online) you merely need to ask for assistance at the check in desk, they'll call for a ramp. If push comes to shove, somebody will lift you up. Total time of the operation = 50 seconds.