If your wearable has the Fidesmo Car Key service installed you can easily activate it as your Tesla key. Please check this article to see current Tesla compatibility.
Follow these steps to activate Fidesmo Car Key:
Step 1. On your Tesla touch screen go to the controls menu and select Locks menu.
Step 2. Click on the "+" button to add a new car. The system will then indicate to place the new key behind the cupholder.
Step 3. Place your ring or wearable on the NFC reader of the car, placed behind the cupholder.
Step 4. Place your Tesla card on the NFC reader of the car, placed behind the cupholder.
If everything went well you should have a new car key in the Locks menu.