We would all be glad to help, but I think we need more
Is the old lockset a cylinder lock or a mortise lock?
If it is a cylinder lock with the hole in the door face too small:
Bore the correct size hole in a scrap piece of plywood. Have
the scrap piece large enough to be able to clamp it to the door
face above and below the old hole. Carefully position the plywood
for proper backset of the new lock. Let the hole in the scrap
guide the drill into the door. A thin scrap on the back side of
the door will prevent splintering as the bit goes through.
If it is a mortise lock, the problem is quite different.
I hope I guessed the problem about right, if not, clarify and ask
Keep the whole world singing . . .
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