Well. I’m not sure I fully understand it. The way I calibrated e steps was to tell it to extrude 100mm of filament and then measures how much filament was pushed through the nozzle. This resulted in a value of about 680 steps/mm.
This always overextrudes and setting it down to 640 steps/mm made it much better.
Setting flow rate in the slicer does not seem to have the same effect.
Lowering e-steps gave the result I wanted but with a lower value than was calibrated for.
If it’s PLA or PETG it’s probably still usable. PLA can get brittle if it’s wet though but drying should make it usable again.
I use a cheap food dehydrator to dry filament.