When powering on Dolby Dimension for the very first time, it will automatically go into pairing mode.  You will see a pulsing Source Light next to the Source Button directly above the Power Button along with a repeating audio tone to indicate pairing.  During typical use, to put Dolby Dimension into pairing mode, simply press and hold one of the three Source Buttons on the right earcup for 3 seconds.  You will see a pulsing Source Light next to the Source Button you pressed along with a repeating audio tone to indicate pairing.  From there, you will need to go to the Bluetooth menu of your Source Device to complete the pairing process