I don't own an AirTag but one showed up on my iPhone.
i dont own one but it showed up on my phone.
[Re-Titled by Moderator]
Showed up where?
If you just got a message saying there was one nearby or traveling with you, then it means there's one nearby or traveling with you, not that it's tied or paired to your device.
It's a notice only.
Follow the steps in the support document you posted from in that case.