Slice and print the calibration model again with the new extrusion multiplier value.

Verify the wall thickness with your micrometer. Repeat the previous steps if refinement is needed.

Do not change the printing temperature during these steps. Temperature might change the flow and therefore the extrusion multiplier.

Tip: The extrusion multiplier is generally constant for a whole spool (if you do not change temperature) but the filament diameter will change. Therefore, before slicing a part, measure the filament diameter you are going to use and enter it into PrusaSlicer.