You’ll need administrator privileges to use these command. You can also run them from a command prompt in recovery

Check Status

manage-bde -status

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.