Step 1: Press and hold the Pairing Button (see image below) on the InCab Alert or Relay for 10 seconds.

(This will put the device into a pairing mode, you will hear 2 beeps and the status light will flash blue indefinitely until it finds a BPU to be paired with)

Step 2: Login to the Blindsight app and open the BPU you wish to pair with.

Step 3: Select "Alert Devices" then "Pair new devices" and you're done!