With the DJI RC-N1 Remote Controller:

Connect your mobile device (connected to the internet) with the remote controller, and then connect to DJI Mini 3 via the DJI Fly app. Follow the instructions in the app to activate DJI Mini 3.

With DJI RC:

When using DJI RC for the first time, connect to the internet via Wi-Fi or a smartphone hot spot, and then follow the instructions in the DJI Fly app to activate the device. After activating DJI RC, connect it with DJI Mini 3 via the DJI Fly app. Follow the instructions in the app to activate the aircraft.