Yesterday，I saw “alxsander shvartsman” on lidraughts（maybe it wasn't him），but today I see he “use computer”.So I want to ask about it.How did you find this？

Hmm
I know how lichess finds out
(I honestly don't know a thing on lidraughts)
But I guess there should be a thing similar in draughts as average centipawn loss in chess
And there is also a reason if you matched your move perfectly with the engine (I guess 5 or 6)
Then it is believed that you are using engine
But I don't think that this will be the case in draughts as possibilities are less
And there are some players who have even higher rating than engine in training like @malacia