How do i tighten the belt after changing my alternator in my 91 chevy silvarado?

I most vehicles, in order to properly put a belt in you have to hold the belt tensioner down (Metal thing about 8%26quot; long that has a pulley on it, and a square hole for a 3/4%26quot; ratchet) in order to fit the belt around it, and when you release the tensioner it automatcally tightens the belt...|||did u un tie it or did it got looser?|||your truck has an automatic tensioner make shure you have the right belt and have it routed correctly if you do and still to loose you will need a new tensioner visit your chevy dealer or summit racing carrys them