A scratched sensor can not be repaired. The only way to 'fix' the camera is to replace the sensor.

In all likelihood, though, your actual sensor is probably not scratched. What is scratched is probably the top of the stack of filters placed in front of the imaging sensor. Unfortunately, replacing a filter stack also requires extensive disassembly/reassembly of the camera that would probably cost more in labor charges than the price of all but the most expensive cameras.¹ Depending upon the specific camera and how it is made, only an already assembled sensor/filter stack combination may be available as a repair part.

¹Many different camera models cost more than a sensor/stack replacement would. But the overwhelming percentage of camera units sold are the lower cost camera models that do not cost more than the labor charge for such a repair would be.

That's not to say the camera is no longer usable at all. Depending on the location of the scratch one might be able to crop all images to exclude the area with the scratch. When selecting a lens to give a desired angle of view and when composing an image the unusable portion of the frame would need to be taken into account.

Depending on the severity of the scratch, assuming it is on the filter stack a few millimeters in front of the imaging sensor itself, shooting at very wide apertures could also minimize its effect on your images.