Hi,
If the recovery key cannot be found, please do not continue trying random repair or reset options, because BitLocker is designed to prevent access without the key.
In this situation there are only two realistic outcomes:
If the recovery key is recovered, the drive can be unlocked and Windows/data may still be accessible.
If the recovery key cannot be recovered, the encrypted files cannot be restored. The PC can still be reused by reinstalling Windows from a USB installation media, but this will remove the existing encrypted data.
A repair shop or Microsoft support cannot bypass BitLocker encryption either, so the key is the deciding factor for data recovery.