How to Convert Color Map/Grid Values

Hi,

Noob here,

I have a software generated Excel report with color map grids that are auto generated with values I would like to change. The grids are usually not symetrical and roughly follow the shape of the area affected.

The color map grid values represent the amount of material removed from a surface. I would like to convert these values to a remaining thickness value based on a known nominal. I've tried the =$A$1-B1 formula with A1 being the nominal and tried to copy/paste or drag the grid but it just copies the new value from that grid to all the others. I've tried Fill and it sometimes fills down correctly but not to the right or left. I've also tried the ARRAYFORMULA but that was a no-go as well.

Most of these formulas and processes were suggested by Copilot AI but nothing seems to work.  I feel that the web based version of Excel is nerfed in some way and even Copilot AI seems to think so and said to contact support.

Any ideas?