How can I fix the handle of my new lawn mower to the machine?

I have just got an Alko 2.8 manual lawn mower but I am having trouble fixing the handle to the machine. The handle appears to be much wider than the machine. I don't know if I should try to force the two sides of the handle closer together to make it fit. If so, I think I will have to get my son's help as I don't think I'm strong enough.