Step 1: Remove the Bad Belt
If the belt is still in place but damaged so it doesn't turn the pulley properly, you'll need to cut it or loosen the pulleys to remove it.
There are usually two bolts holding the alternator in place.
Sometimes it's hard to find both of them, especially in new vehicles that are crowded with complications and you shouldn't own.
Step 2: Install Pantyhose
As seen in the video, stretch out the pantyhose as far as you can and run it around the pulleys.
Use multiple layers if you can, to really fill the pulley with material so it gets a good grip.
Tie it off with any knot you like.
Cut the tails short.
Drive your car.
Step 3: Install New Belt
If you ever decide to get a replacement belt, here's how to tighten it properly.
Use a crowbar or other lever to pry the alternator and tension the belt.
While doing that tighten the bolt with a wrench.