Combination it is a very involved process to reset the lock to accept a new combination. Back be removed, the lock disassembled, the combination chamber removed and the tumblers reset. FYI, if they don't have the keys a locksmith can not just make a key.
The over ride lock core will have to. The item "Kaba Simplex Ilco Unican 1021 Pushbutton Lock Over Ride Core Installed withKeys" is in sale since Tuesday, March 06, 2018. This item is in the category "Business & Industrial\Construction\Building Materials & Supplies\Doors & Fixtures\Locks & Locksets". The seller is "bake98" and is located in Oxford, Pennsylvania. This item can be shipped to United States.