Browse the pre-loaded database. If your game isn't there, the "Fixed" version makes it easier to manually add new hex codes. The "Swap" Trick: If playing on physical hardware via OPL, ensure you use the "Enable Cheat"
Codebreaker, OPL, and SMB Tutorial Using FMCB (2020) : r/ps2
Depending on your setup, the process for using the ISO varies: On Original PS2 Hardware (FMCB/OPL)