You’ll have to open up an AirTag and reset if it’s been used and the previous owner didn’t unpair it. Why? An AirTag can be associated with one Apple ID.
If you want to use an AirTag that someone else has used, they need to remove the AirTag from their Apple ID first. If the previous user removed the AirTag from their Apple ID but they were out of Bluetooth range of the AirTag, then you need to reset it before you can use it with your devices. Here’s how:
- Press down on the polished stainless steel battery cover of your AirTag and rotate counterclockwise until the cover stops rotating.
- Remove the cover and the battery.
- Replace the battery.
- Press down on the battery until you hear a sound. This sound means that the battery is connected.
- When the sound finishes, repeat the process four more times, removing and replacing the battery, then pressing down on the battery until you hear a sound. You should hear a sound each time you press on the battery, for a total of five sounds. The fifth sound is different from the previous four. This indicates that the AirTag is now ready to pair.
- Replace the cover by aligning the three tabs on the cover with the three slots on your AirTag.
- Press down on the cover.
- Rotate the cover clockwise until it stops rotating.
(This how-to is based on my experiences and info on Apple’s support pages.)