my iphone 7 plus has scratches on its back and i would to have it repaired?i have apple care+ i just want my phone to look brand new

We are just users like yourself and can't speak for Apple. I would:

Contact Apple for support and service - Apple Support

I would add that scratches and such are usually classified by Apple techs as "cosmetic damage" and are not covered by warranty. Maybe, if you have AppleCare+, might be able to file an "accidental damage" claim and get a replacement, but it is a big maybe and I would not get my hopes up too high.