You have to prove it. How you do that after the fact is difficult. Democrats pulled a fast one in Wisconsin and Michigan and got away with it
Obvious what went on in those states.
They stopped the count in Counties they knew were for Biden, let the other counties finish their count, knew how much they needed to make up in votes,
then took out votes for Trump and added votes for Biden. It is pretty obvious based off the lead Trump had and amount of votes left around 1-2 a.m.
What you do now, I have no idea. Short of someone admitting or having video of that happening there is nothing you can do