This step is pretty self-explanatory. You either need to buy a pre-assembled PCB or solder all the components on the board yourself.

Plug in a LiPo battery that fits the back side of the PCB. Pay attention to the polarity of the cell and make sure you're using a protected battery, this is absolutely crucial for safe operation! Most batteries that fit will have a capacity around 250 - 350 mAh or less if you want.

Plug in a USB-C cable to start charging the device. It will light up red until it's done charging, when the LED is off you can remove the charging cable. Charging depends on your battery size, but in most cases it'll take 1 - 2 hours.

Mount the tracker to your headset either by using some cable ties with the mounting holes on the PCB or just simply sticking something like velcro tape to the back side.

Turn on the device by using the switch. If it's on, the LED will light up green and you should be able to see a very faint red glow on the LEDs. Have fun!