replace motherboard and now need BitLocker recovery code

Welcome to the Dell Community @Zeke1906 

If the information on the HDD is not needed then just erase the drive and reload the OS.

Best regards,

U2

If the system was tied to your Microsoft account, it's accessible from there.

https://support.microsoft.com/en-us/windows/finding-your-bitlocker-recovery-key-in-windows-10-6b71ad27-0b89-ea08-f143-056f5ab347d6

If not and you don't have a backup/record of it, as long as you have your data backed up elsewhere, simply do a ground-up reload of Windows:

https://www.dell.com/support/article/en-us/sln297920/reset-or-reinstall-windows-10-on-your-dell-computer?lang=en

Ps the asset 

@Zeke1906  You shouldn't post your Service Tag on public forums. At a minimum, people could use that to submit ownership transfer forms for that system, which can make it more difficult for you to get warranty service.  And the Service Tag doesn't help with this situation anyway.  The BitLocker Recovery Key is randomly generated each time you enable encryption on a partition.  If you were to decrypt and re-encrypt the partition, the Recovery Key would be different after the second encryption.  As has already been said here, if you can't find your Recovery Key backed up to the cloud in your Microsoft account and are sure you didn't save it anywhere else, then your data is effectively gone.  There are no backdoors.  The reason you're seeing this after a motherboard replacement is that the TPM chip on your original motherboard had a decryption key for your Windows partition.  When BitLocker is enabled, you're prompted to back up the Recovery Key to your choice of a few places in order to make sure you can access your data in exactly these kinds of scenarios.  However, Dell does ship some systems with BitLocker "pre-staged", meaning with encryption enabled but in a suspended state so that the partition acts like a regular unencrypted partition.  If you choose to link your Windows account to your Microsoft account, then the Recovery Key is backed up to your Microsoft account and then the encryption is fully enabled.  Or at least that's how it's supposed to work.  Again, if you don't have the Recovery Key in your Microsoft account or somewhere else, then your only option is to set up Windows from scratch and restore your data from a backup that you hopefully have.