Hello Travis Roark,
thank you for posting on the Microsoft Community Forums.
In your case, there are two solutions:
Solution 1: Ask the Seller for BitLocker recovery key. If he lost it, let him follow the steps in Finding your BitLocker recovery key in Windows - Microsoft Support to recover.
Solution 2: If retrieving the recovery key from the seller is not possible, your next step would involve resetting the device, which will erase all data on it. About the details about using installation media to reinstall Windows, please visit Recovery options in Windows - Microsoft Support.
Windows 10: Download Windows 10 (microsoft.com)
Windows 11: Download Windows 11 (microsoft.com)
Hope it helps.
Kind regards,
Lei