Replace a Shower Diverter Valve
Otherwise, replace the diverter stem completely. You’ll need to take the old stem to the plumbing supply store so you can be sure to get an exact replacement. The new diverter valve slips right into the pipes just like the old one that you pulled out. (Be sure to use the faucet grease.)
Reverse the removal procedure to finish the repair. Turn on the water supply and test for any leaks.