What brand & model of filter is it? I
Troubleshooting filters isn’t difficult.
Start by taking the filter apart & make sure there isn’t something stuck somewhere it shouldn’t be.
Make sure there aren’t any cracks in the uptake tube.
Remove the impeller from the motor.
Gently clean the impeller. If it has a removable shaft in the middle, remove it & inspect it for signs of rust or wear. It might need a new one.
Inspect the blades on the ‘fan’ to be sure each one is intact & present. If any are damaged the blade assembly needs to be replaced.
Clean the uptake tubes & weir and rinse out the filter box & media.
If you have it, rub a thin layer of food grade
silicone grease on the impeller shaft or in a pinch, mineral oil or Vaseline can be used. But you shouldn’t be able to see the oil or Vaseline except as a shine.
Put it back together. fill with water & try it out.
Hopefully it’ll be as good as new.