OP asked about the tribulation, when is (was) the great tribulation.
“1000 years” isn’t a literal span of time; IIRC that’s in the book of Revelations, which has symbols and patterns.
Christ defeated Satan & his minions at Calvary.
He reigns now.
‘Christ appear to everyone ‘ is in the book of Revelations also, at Judgement Day.
So where does all the sin in the world come from today? Is Satan in chains currently?