If Covid-19 virus seriously affects USA how will this skew the voting this November?

It would affect the urban areas the most. I would expect urban voter turn-out to be lower unless one party had a high number of absentee ballots. In some areas the turnout of those most affected would be in record numbers (even if deceased), all voting for one party regardless of prior party affiliation.
Rural, Fly-over, Farm country would be hit the least.
Or as on writer put it, "Catastrophe Strikes: Poor Hit Hardest", John Ringo, "The Last Centurion" .

 

Unless the dead and seriously ill send in absentee ballots. Then there could be a Democrat landslide.