1.open the emulator
2.press the toolbar (where it write PSX4m-GUI) and choose "GUI config"
3.press on "ROMS DIRECTORY" and select the folder where you have your isos.
4.restart the gui (close and reopen).
5.choose the game and press "configure" and at core choose "PCSX-REARMED" if its not already. Now press "X" and click save.
6 Now press play and enjoy