There are two Apple Stores in Istanbul. Other than that I'm not sure.
https://www.apple.com/tr/retail/zorlucenter/
https://www.apple.com/tr/retail/akasya/
It's also not a given that they can or will replace the battery. Apple has repair terms for iPhones that they may restrict service to the country of distribution, which may be an issue with regulations. I understand in some countries that Apple only allows their Apple Authorized Service Providers to do complete exchanges with service replacement devices.
Apple does have designated AASPs in Pakistan. Is there an issue working with them?