I did this process years ago. Bought a new cylinder & cylinder parts from S&W and sent them to TK to have the 2nd cylinder reamed to 9mm. Because I'm lazy I only use one 9mm load for all semi-autos, revo, and PCC.
You don't need a 2nd cylinder ... you can send yours to TK, have it reamed, and shoot 9mm or 38/357.
https://tkcustom.com/pages/9mm-rechambering