The handle on the mower should not be hard to replace. You will need a pair of pliers and a wrench. Remove the old handle and lay to the side. Replace with new handle and attach the throttle from old handle to new handle. Make sure all attachments on handle are working.
If it's a push mower, this is not hard to do. there should be several bolts where the handle touches the base mower part. You simply unscrew these to take the handle off, then rescrew these in with the new handle in place.