Really need model # to help.
To put the belt back on, remove front panel and check idler pulley, probably busted or has a bad bearing.
If ok, just rout the belt around the drum with the grooved side against the drum
and placed at the wear mark on the drum.
Reach under the drum,put the idler pulley spring metal into the slot in the frame by the motor pulley. Rout the belt around the pulley and onto the motor pulley.
The belt routing will look like an S. There is ONLY one way belt will go on and keep the tension for the motor to turn the drum.
Also, if your idler pulley is a slide instead of a wheel, throw it away and buy the standard plastic roller type, part # 691366