You connect the charger port for power. That's basically it. Kinda the same like using it normally when you're out of battery. Just that this time you won't charge the battery or degrade the life of the battery, and it runs cooler since it doesn't charge the battery or us it anymore.
Edit: I was watching this video, and it was pretty easy to do. Basically I'll remove the connector from the battery when using on the desktop, and connecting it back when using it on the go, a little hassle but worth it.
Just use an allen key to open it up. Open it up slowly upside down so the marbles parts won't fall off like in the video, and just remove the connector slowly, and close it up.
You can also replace the battery easily, if you ever want to change it, or just remove it completely if you're using it for desktop only.
I feel its too much of a hassle to open it and better to get a separate Desktop DAC