Help! c240 belt
 

The idler pulley fell apart on my 2001 C240. This took the Serpentine belt with it.
New Pulley and new belt today from MB. I can't figure out how the belt goes, there seems to be too much slack, I've tried several ways. Also is there a special tool to pull back the belt tensioner? I really need this thing running by Monday.
Thank you! BKH