1. First of all, make sure that your watch is powered off and that you take off the bezel from the watch. The bezel is the elastic frame around the watch body.
2. On the left side of the watch, you will find the SIM slot. Open it.
3. Introduce the SIM card in the SIM tray; the shape of the tray will help you place the SIM card in the correct position. Make sure that the metallic contacts of the SIM card are facing down, like in the picture.
4. Once the SIM-card is properly inserted, turn the watch on. After a few seconds, you will see a full signal bar on the status screen of the watch. This may take a few seconds.