You can book an appointment at the Apple Support Page or through the Apple Support app. They usually finish the swap in about 1–3 hours.
Local independent shops are often the fastest option, but there are trade-offs to consider. Self Service Repair - Apple Support can you buy a new battery for an iphone
If you’re tech-savvy and want to save a bit of money, Apple has a Self Service Repair program for newer models (iPhone 12 and later). You can book an appointment at the Apple