Dear aaronkellyuk
Hope you are doing great, I am aware of the present situation is that your device has became inaccessible and suffering the issue of BitLocker error 8007139f .
With great effort of inquiry, BitLocker are beyond the supported scope of community, From some threads in the Microsoft Learn community, this error code may be related to TPM (Trusted Platform Module) or UEFI Secure Boot settings.
For the most appropriate community for posting your issue shall be Microsoft Learn, which it is a professional place consist of many technical experts or advanced users like you. Moreover, I will keep this thread opened in case our MVP/Volunteer moderator/ can have some targeted insights for you.
Best regards,
Chandy|Microsoft Community Support Specialist
* Your patience and cooperation are highly appreciated.