Print a single-wall cube, measure the wall with calipers, and get the corrected flow rate (extrusion multiplier) for your slicer.
New flow = current flow × expected ÷ measured. Print a single-wall object (vase-mode cube) with a known line width, measure each side with calipers and average them. Calibrate e-steps first; flow fine-tunes on top of a correct extruder. In Cura this is Flow, in PrusaSlicer Extrusion Multiplier (1.00 = 100%).
Print a single-wall cube with a known line width (say 0.45 mm), measure the walls with calipers and average them, then new flow = current flow × expected ÷ measured. Measuring 0.48 mm against an expected 0.45 at 100% flow gives 93.75%.
E-steps calibrate the extruder hardware (how many motor steps push 1 mm of filament) and live in the firmware. Flow is a per-material fudge factor in the slicer on top of that. Calibrate e-steps once per printer, then flow once per filament type.
Cura calls it Flow (percent), PrusaSlicer and SuperSlicer call it Extrusion Multiplier (1.00 = 100%), OrcaSlicer has Flow Ratio. Enter the new value there and reslice.