Once you have obtained a BIOS file, installing it in PCSX2 is relatively straightforward:
Locate the BIOS folder : Open PCSX2 and navigate to Config > BIOS/Plugins
Add the BIOS : Click on "Browse" and select the BIOS file you downloaded
Configure settings : Adjust any necessary settings, such as region or console model, to match your BIOS
Save and restart : Save the changes and restart PCSX2