You'll need an app to do that. Download one like Bimmerlink and get a compatible adapter. I used the ODBLink CX adapter as it was cheap.
Make sure the parking brake is not on, you'll have to turn the car to disengage the parking brake. If you're parked at an incline, you should park somewhere flat. Also make sure you're using wheel chocks or have something else that blocks the car from rolling.
Put the car in either "drive ready" mode or running, then insert the adapter into the OBD port. Next, connect to the adapter from your phone and open Bimmerlink which will take a little while. Once connected, you should see the parking brake icon toward the bottom. If you don't, close out of Bimmerlink completely and open it again and it should show up. If it does not, maybe you are not using a compatible adapter - ODBLink CX is compatible and seems to be the cheapest option.
Once you've opened up the parking brake screen and without using the brake pedal or parking brake, tap the Activate option. Once started, it'll put the car into diagnostic mode, start retracting the parking brake motor for 10-15 seconds, and will tell you once completed. Mine likes to say it failed, but it still worked. At this point, you're ready to work on both of the rear calipers.
- this is a good video to use as reference. You skip disassembling the parking brake motor and just slowly compress the pistons. It's not written out explicitly but make sure you have a thin 17 mm wrench for the counter-hold nut on the rear calipers.
Once the rear pads are replaced and everything is reinstalled and torqued properly, you need to go back to Bimmerlink and click to disable the parking brake service function. You should be able to hear the parking brake motor running for 5 seconds or so, but not much longer. After it give you a message that it was done successfully. You can turn the car on, use the brake pedal gently but fully a few times, then turn on the parking brake as a test.
There is also a service function which will show you when everything monitored is due for replacements. In there you can update the rear brake service. If your brakes ever got really hot, it's likely the plastic on the brake pad wear sensors has fused to the brake pad making reusing that sensor nearly impossible. It's also possible to break the sensor when removing it or if it broke due to wear. In that case, the rear brake pad wear senor must be replaced and you might not be able to reset the service until done.