remove what?
How to multiple remove on lichess.
I assume you meant how to multipremove. Go to https://lichess.org/account/preferences/game-behavior then go down to Input moves with the keyboard, then click Yes. 
There's no comparisons being made, so there's absolutely no reason for a lock.
People, however, tend to get into comparisons once the subject is breeched and that's when a lock should reasonably occur.
HOW????????????????
Sorry if this is in the wrong category.