Step 1: Remove the Bad Belt
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
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
Use a crowbar or other lever to pry the alternator and tension the belt.
While doing that tighten the bolt with a wrench.