Mac Reset Password

When we set up my partners Macbook Pro in 2017 we were asked to enter a number or password for if a reset etc was ever needed in future.

This was not her usual admin user password adn at teh time we took a photo of what we chose. Just doing some admin now and we can't find that number/password. Does anyone know the actual name of what this is called and where we can reset it from?

Just to note we are not locked out and are still using the Macbook as an admin user just want to make sure we are sorted for the future.

Thanks,

Sam