Hi @Peter Wojtasik ,
there are a couple of option to find the Bitlocker Recovery Key:
Find your BitLocker recovery key
If you can't find the Bitlocker Recovery Key or password there is no chance to get access to the data on the external hard drive.
What if I can't find the recovery key?
If your device is managed by an organization, check with your IT department to retrieve the recovery key.
If you can’t find the BitLocker recovery key and are unable to undo any changes that caused it to be needed, you’ll have to reset your device using one of the Windows recovery options.
Resetting your device will remove all of your files.
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Regards
Andreas Baumgarten