Don't make any changes to the partition. Avoid writing any new data to the drive to prevent overwriting potentially recoverable files.
If you have a Microsoft account, check https://account.microsoft.com/devices/recoverykey
Try using the BitLocker Repair Tool:
Open Command Prompt as administrator
Run: manage-bde -repair X: (replace X with your drive letter)
You may now Right-click the encrypted drive
Select Properties > Tools > Error Checking > Check
You may also consider third-party data Recovering Applications.