If he were here now, he would corrects me. - nie może być corrects. Po would jest zawsze bezokolicznik, tak jak po innych modalach.
If he were here now, he would correct me. - ok.
If he were here now, he would corrected me. - nie może być 'ed' bo patrz wyżej.
A najprościej mówiąc 2nd conditional:
If + past simple, would + bezokolicznik.