I bought a new craftsman garage door opener and it didn't come with the keypad entry (outside). I want to use my old craftsman outside entry. How do I reset the code to match my new opener?

The old keypad likely needs to be compatible and you didn't state how old it is. Through about 1992 the codes were set with a series of switches; through about 1997 they went to a billion code setup; then switched to a rolling code set up, which is what you have now.

Look at the instruction manuaI section "Programming". I installed my Craftsman in 2004 and it detailed programming a keyless entry, even though it didn't come with one. You might try following the programming instructions just to see if it works, even if it is an old keypad.