Hello kaydee258,
Thank you for posting to Apple Support Communities.
We understand you're having an issue setting up AirTag on your new iPhone. Make sure you're using the same Apple ID that you were when you set the AirTag up initially.
Additionally, make sure that your iPhone is updated with the latest version of iOS. Before updating, we recommend backing up your iPhone first. These articles can be of help. When you back up, you can back up using a Mac or PC rather than iCloud if you choose.
How to back up your iPhone, iPad, and iPod touch
Update iOS on iPhone
Then, test if the issue continues. If you are using a different Apple ID, this article can help: If an item or device is connected to another Apple ID - Apple Support
Learn how to reset your AirTag if you need to do this: How to reset your AirTag - Apple Support
That should help. Let us know if you have any questions.
Take care.