How do i reset the tensioner on the serpentine belt on a 91 chevy astro?

all you have to do is pull back on it to re-set it ,unless its out of place ,and if it came apart,you may as well buy another one,their to hard to get back together,but to put the tension back on it,all you have to do is pull back on it,and place the belt behind it,then when you start the vehicle the tension will automatically be set,good luck with it.