Is there a fee to help change iPhone 7 Plus battery?

Yes, probably. this is an official apple forum, so we can tell you to go find and talk to an AASP (apple authorized service provider) or make an appointment at your local Genius bar at the Apple store in your town/city/region. that's pretty much it....if you want to find out about the last bit, and the first sentence, then you might want to ask your question on other iPhone forums, just not on an official Apple forum....... iFixit might be interesting......

good luck

john B

Apple will not install a part you bring to them.

Apple will only replace your battery with a part they supply.