How do u tighten a serpentine belt

You have a single serpentine belt that drives all accessories. It is kept within specified tension limits by a tensioner pulley. There should be a point on the pulley assembly and an indicated range on the front cover where the tensioner pointer should fall into. If it does not, the tensioner and/or spring needs replacement.

Here is the general information, and 2 diagrams; one for the 2.0L and one for the 2.3L, since I did not know which one you have.
You might also check the condition of the belt as if it is cracked or worn it can stretch beyond service limts. Also, check accessories including idler pulley for play at the pulley as this indicatesa a failed bearing.