You have 3 bolts the front two one on top one on the bottom are pivot bolts loosen them both.
Then loosen the third bolt that is the one closest to the firewall on top of the alternator. Take a long pry bar and push down on alternator to tighten belt it should move with all the bolts loosened up.
Keep the pressure on and tighten the third bolt closet to the firewall.
That should hold tension on belt now finish tightening the other two.
The bolt on bottom is tough to get to may have to take tire off to gain better access.
Then loosen the third bolt that is the one closest to the firewall on top of the alternator. Take a long pry bar and push down on alternator to tighten belt it should move with all the bolts loosened up.
Keep the pressure on and tighten the third bolt closet to the firewall.
That should hold tension on belt now finish tightening the other two.
The bolt on bottom is tough to get to may have to take tire off to gain better access.