How can I fix a Indesit IS70C Tumble dryer belt that isn't snapped?

I have opened up a friends tumble drier that wasnt turning, Found the problem - belt come off spindle, but when I re attach it isn't turning the drum, the spindle (that is next to the motor) doesn't feel tight on drum, tried it in few places on the spindle and motor to see if tighter - tightest to left but seems naturaly it is ment to be centered on the thread on the motor that belt is attached to. The drum does feel tight when i try to turn from inside the drier but on the outer drum it seems to turn easier. Do I need a new belt that is tighter or is there somthing simple that I am not doing? Please Help me