To replace a broken shovel handle could be easy once the rivet and handle are removed and the new handle is inserted with wedges.
Remove the old shovel handle by drilling out or sawing off the rivets.
Taper the end of the new shovel handle to fit into the shovel head.
Make sure that the handle is seated all the way down and that the holes in the handle and the shovel head align.
Insert rivets or bolts to attach the handle to the shovel head. When choosing a new shovel handle, make sure that it is the same length and diameter as the old handle.
If you are using a fiberglass shovel handle, be careful not to over-tighten the screws when attaching it to the shovel head. This could damage the handle.