Can I replace battery on iPhone 6S plus?

Yes. Read the details in: iPhone Battery Replacement - Official Apple Support

Just go to a authorized Apple service provider. they quote before changing your batter so you know how much you pay in total

I need to replace my battery in my i phone 6 plus

There are no Authorized Apple dealer in my area I live in Columbia, SC all Apple dealer store are closed

This is like talking to a wall....SAD unprofessional

Then call AppleCare and arrange for mail in service.

Apple did not cause the global pandemic.