Can't you look at the other handle to see how it is put together?
On my older Craftsman table saw that handle spins within the main portion. There is a thin flat washer on the left end. That nub is peened out to hold the washer on.
If yours is meant to spin, would a circlip fit on the end? You could drill a hole in the left end and install a washer with a self tapping screw to hold it in place also.
If it is just a press fit as mikegt4 states, just tap it in, maybe with some adhesive. Or, grab that end with some good sharp pliers to create some raised ridges that will grab and hold it in place.