The ME/CFS Society of NSW Inc.

Method 1:
Find anyone who can help you lift the thing down of the wall and carry it to somewhere that you can lay it face-down on the floor.

Unscrew and remove vent cover and fan belt cover. Remove fan belt. Unscrew and remove entire back plate.

Note that the belt tension wheel, not being under tension any more has randomly located itself anywhere in the bottom of the machine.

Lift drum out to remove the remains of the old belt.

Spend half an hour, without diagrams, figuring out how the belt tension wheel is supposed to be fitted and threaded.

Carefully lower the drum back in so that it fits into the front "slides" properly.

Using all four hands, hold the new belt in roughly the right position on the drum, thread a loop through the tensioner and fit that loop over the drive pulley.

Still using all four hands to keep the belt in the right place, use fifth hand to attach tension spring to base.

Swear because it fell off and you have to start over.

Once you have the belt under tension, and the tension spring attached properly, you now only need three hands to gently rotate the drum while ensuring that the belt does not slip off the tension wheel. Two complete rotations should be enough.

Refit back panel, alighning rear "slides" with drum. Swear because there are three screws missing.

Attach new fan belt as well (better safe than sorry). and go in search of screws that will fit belt cover and air vent.

Now that your back is killing you and at least one of your hands is shredded from trying to get the tension wheel bit right, find someone else silly enough to help you carry it back into the laundry and lift it back into place.

Method 2:
Get someone else to do it.