Please see the attached article for fixing some possible reason/s for under extrusion.
Other Possible reasons for under-extrusion:
logged or Partially Blocked Nozzle
Incorrect value for Extruder Calibration
Incorrect Printing Temperature
Filament Quality Issues
Over-tightened Extruder
Worn or Slipping Drive Gear
Hotend Insulation Issues
Under-Sized or Poorly Installed Bowden Tube
Inconsistent Filament Diameter
Extruder Motor Issues
Inadequate Retraction Settings
Overheated Stepper Driver or Extruder Motor
Wrong Slicer Settings (Flow Rate or Multiplier)
Incorrect Print Speed
Filament Path Obstruction
Partial Heatblock or Heat Break Failure
Cold Weather or Low Ambient Temperature