Serpentine belt

Just to be clear you were changing the belt and the tensioner pulley was loose or a different pulley was loose.

If it was the tensioner, here is a guide that will help with this:

https://www.2carpros.com/articles/serpentine-belt-tensioner-replacement

https://www.2carpros.com/articles/replace-serpentine-belt

Please find the info below from the manual that will help replace both the tensioner and belt as well.

Let us know if you need more info. Thanks