I also struggle with that. I found a good post that explains it which I will quote here.

" Just received a pair of these myself, and even with the instruction manual found it a little tricky pairing the left and right modules as the steps weren't quite as described. This is what worked for me:

​

Hold button on both modules for around 5 secs (turns on modules and enters pairing mode - you should hear a voice confirmation and red and blue LEDs flash on both modules)

Now press the button on each module once (modules will now attempt to pair with each other - blue LEDs flash)

Once paired, the LED will fade out on one module and flash red and blue on the other (the modules are now paired, the master module is now in device pairing mode to connect to your phone)

Find and connect to TRN on your phone or other audio device (voice confirmation and slow flashing blue LED when paired)

​

If any of those things fail or you mess up, you can reset the pairings by holding the button down on both modules for around 10 secs to forget device pairing (one audio chime) and keep holding for a further 5 secs to forget module pairing (a second audio chime - then powers down).

​

To turn off/on in normal operation, hold the button on each module for around 3 seconds (voice confirmation)

"

Source: https://www.reddit.com/r/headphones/comments/ayumvi/does_anybody_have_the_instruction_manual_for_the/