How do I find the code to unlock the door?

use your spare key .

Have a 'cheap key' made just to unlock the doors and keep it hidden under vehicle somewhere.. Since you have to have the doors open already to find the *factory default* code, check this out: https://youtu.be/ZBANE1nhZQg

The code on the door is set by the owner, there is no way to know it unless you can reach the prior owner.