Hi @Heather_t21 it's possible you got something that had been returned. Have you asked the people at The Source? They should be able to tell you if they are selling refurbished units.
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Welcome to the Fitbit Community, @Heather_t21. I'm sorry to hear that you see old Inspire 3 Sleep data when you log into the app.
When you set up a new device all the information that you find in the app is yours. Was the mentioned information registered before you set up your tracker?
Even if the device was previously used or refurbished, this information shoudn't show up on your account.
I'd suggest following @Odyssey13's advise.