Put a new belt on the washing machine with a Park tyre lever as it was bloody tight. When twanged it's a very high note. No tyre lever, no washing machine.
Assuming you have the right belt, then the way to do this is not with a lever or indeed any tool.
You need to rotate it on, much the same as picking up a dropped chain onto a chainring using the front mech.
Put the belt round the motor pulley, then get it as much started onto the drum pulley as you can by hand.
Then, rotate the drum by hand to roll the belt up onto the pulley.
The diameter of the drum is large enough that you can generate a lot of leverage.
Another approach that can work ( depending on what you can get access to ) is to use a ratchet-strap.
Wrap it around the outer drum housing and around the motor body, and ratchet it up to pivot the motor on it's pivot towards the drum.
You are working against a very powerful spring on the motor pivot, but the ratchet strap will compress the spring enough to allow you to get the belt on.