Edward,

The easiest way, if the gun has a removable choke, is to change the choke.   If the barrel is solid, then changing the choke is a very technical chore that I’ve never attempted.  I’d recommend leaving that task to a skilled gunsmith or simply using another gun.

Each state has different regulations.  Most states don’t allow the use of .22’s for turkey hunting, but you will have to check the regulations for the state where you plan to hunt.  You should spend some time testing the pattern of your shotgun at different distances and you will learn at what distances the pattern is appropriate for turkey hunting.  My daughters use a youth model 20 gauge and it holds a good pattern to approximately 25 yards.  That’s far enough that my oldest daughter, Raleigh, harvested a mature tom last year!

Growing Deer together!

Grant