Use the Pre-ADC gain together with the gray ramp to find the highest setting without clipping the brightest bars. Then adjust fine gain.
Use individual color gain to adjust the color balance. I use a capture card for calibrating but you should be able to use the OSSC mask feature on your display. Set OSSC mask to full white or just below full white then use the 240p white screen test and match the intensity with the custom color settings. Then adjust OSSC fine gain to match the color to the mask color.
Offset is used to adjust the black level. You can use the gray ramp and make sure the darkest bars are distinct. I haven’t needed to change the default offset yet with my consoles.