How can I fix scratches or cosmetic damage on my iPad Pro?

Cosmetic damage will not affect the functioning of your iPad's Camera. If the camera lenses themselves are undamaged, you have no need of an expensive repair.

Be aware that for practical purposes, in lieu of repairing and returning your own iPad, Apple usually exchange the iPad for a renewed/refurbished iPad of the same model and specification. The cost of the exchange is the same as would otherwise be charged for repair. Unless you have benefit of an active AppleCare plan, an out-of-warranty repair will be expensive.

As for out-of-warranty repair costs, Apple offers a fixed-price price repair - in many cases, this can be up to 70% of the as-new cost of the iPad. You can verify repair eligibility and cost for your region/country here:

iPad Repair & Service - Apple Support

Cosmetic damage is not considered a fault - and therefore is not "repairable".

If you have benefit of an active AppleCare+ plan, in a country where this optional cover is available, you might be able to make a claim for accidental damage. AppleCare+ is an insurance product that provides cover for non-warranty and/or accidental damage; using this service incurs a small excess/deductible fee.