Revolver pistol alignment?

I recently was passed down a H&K 922 .22 lr pistol. I took it shooting for the first time in about 25 years and put about 25 rounds through it and it shot fine except for a few misfires which can be expected with a .22. My friend that i was with asked to shoot it so i loaded it up and on his third shoot the cylinder didnt line up and shot the metal to the left of the barrel and two pieces of lead went into his face (hes fine). Does any one know how to fix this?