Bosch WFB 1605 replacing a fan belt myself?

I'v a Bosch WFB 1605 front loading washing machine. It stopped spinning, but everything else seems to be working. Noticed that the fan belt had slipped off, however, when I try to put it back on, the fan belt seems to small to stretch around the wheel. And I don't seem strong enough to stretch it on. Is there a special way of putting the fan belts back on.
any help very appreciated. thanks.