[Quoth]

I doubt the surface can be swapped. Try toothpaste (not gel kind) or headlamp scratch removal kit.
Test whatever on a CD case first.

Depends how deep the scratch is. A lot of polishing without pressure to avoid cracking substrate!

Also eink panels vary and have a calibration factor put in factory part of firmware that's not updated which users can't easily access. Just swapping the panel is a significant cost and often poor contrast. At least it's not cracked.

Edit:
That looks like a risky repair even if it does apply to a PW3 (gen 7) Kindle. I'd wonder if there is any front light after.