Battery replacement

I prefer Apple Stores, and this is the closest.

Square One - Apple Store - Apple (CA)

Start here:

Official Apple Support

Click on iPhone, then Repair Options, Get Service, Battery & Charging, Battery Replacement, Schedule a Repair, enter your serial number or IMEI, enter your location and carrier (or no carrier), and pick a location. I'm in the San Francisco Bay Area, so I won't be able to see what you see, but I have a variety of options including Apple Authorized Service Providers and a few Apple Stores with varying appointment times.

There may be other ways, but that's how I just went through it. It could be different in your region and there are other ways to make an appointment, such as a lookup of your devices.

I gave it another try from here, which will be easier if you're already logged in with your Apple ID that you use for the iPhone.

Get Support

From there you'll see whatever devices are associated with your Apple ID. Click on your iPhone, Battery & Charging, Battery Replacement, Schedule a Repair, enter your location and carrier (or select none), and select a location. For you I'd recommend the Apple Square One location, but if the appointment times are inconvenient I guess the closest stores might be in Toronto.

Good luck with it.

Where are you located?