Remove lid
Remove back, including fan / heater cover (all screws and central pin)
Remove fan blades
Remove drum
Place belt over drum and motor arm
Only then, lift (two man job) the drum back into place (at front)
Hold in place as second person replaces back of dryer - make sure the spindle comes through the back - drum is now in place
rebuild in same order as you removed
job done - not easy!!
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix tumble dryers.