Replaced Alternator, Unsure of how to fit belt back on?

I took out my old alternator and just untightned the tensioner on that to pull the belt off, however once I put the new one back in I had to have the alternator unbolted then force it back into place to put the pivot bolt back on. Once on I could not even feed the tensioner bolt back into the top of the alternator due to the belt already being so tensioned, it moved the top of the alternator just above where it needed to sit on the side of the bracket the tensioner sits on.