Is this sudden? Has it worked before?
If it was worked but suddenly started acting like this, It could be that the shaft of the stepper is broken or otherwise not connecting properly to the extruding gears.
Could also be a dead channel on the driver or broken wire for a set of the coils in the stepper.
I would start by disassembling the extruder and see if the motor rotates properly. If it doesn’t, then check wiring from driver to motor. if wiring is OK then it’s probably the driver that’s dead. edit it could also be a dead stepper motor, try running it from a different driver to see if it works at all.
If it does move properly when disassembled, check shaft that connects it to the gears.