If there was an existing account on that device when you purchased it, then you will not be able to find the associated Bitlocker Recovery Key, it would be stored on the previous owners Microsoft account online.
A Windows reset will not work on an encrypted drive, the only way to remove the drive encryption and make that device your own is to create a bootable Windows USB on an empty 8GTB USB flash drive, then use that to clean install Windows and at the start of the installation process, delete all partitions on the drive.
Click this link: https://www.microsoft.com/software-download/windows11
to download the Media Creation Tool (Click on Download Tool Now), with that you can create a bootable USB flash drive (min 8GB) using that tool
Then, Boot your PC from the Installation Media you just created to begin installing Windows 11.
During the installation process skip the steps which ask for a product key and select the option 'I am Reinstalling Windows 11 on this PC'.