Don’t get the V-belt on it

Hi, I’m just about to swap the V-belt and the V-belt for the first time (for me, not for the car). I now have both belts off and wanted to pull the V-belt on it. However, I can’t get it over the disc on the alternator. It’s missing a little bit. I ordered it from I.L. Motorsport for the NA of course. Can it somehow be related to the fact that the belt was in the car overnight (below 0°)? EDIT: alternator and the tensioner is of course solved, otherwise I wouldn’t have got the old strap off either.