If you forget BitLocker password, you can still unlock the D partition by BitLocker recovery key, the recovery key can be found in some place:
In your Microsoft account, On a printout you saved, On a USB flash drive, when you enable BitLocker you have three options to keep recovery key.
Unfortunately, if you've lost your password and your recovery key, then there is no way for you to access the data protected by BitLocker.
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