It's a fair question. I'm in New Zealand, which has no Apple Stores, and I'd like a new battery replacement for my old iPhone 6Plus my wife is using.
Where/Who do I take it to? How much will it cost? I tried looking on the Apple NZ website but it's useless.
The Apple response, and offer, only covers the USA so far...
Not true! Most countries where Apple has stores the process is the same. You should contact an authorized service center and the must know by now.