You’ll need administrator privileges to use these command. You can also run them from a command prompt in recovery
Turn off Encryption
manage-bde -off C:
Change C: to the drive that has BitLocker on it. Check with the status command. May not be C if your in recovery.
Also note that after the encryption is turned off it takes awhile to decrypt. Check with status command
Unlock BitLocker Encrypted Drive
manage-bde -unlock C: -recoverypassword 11111-...-99999
Replace C: with actual drive
Replace the numbers at the end to your actual recovery key.