This key is usually saved to your Microsoft account, a USB drive, or printed when BitLocker was first enabled. Please try signing in to your Microsoft account on another device and check:
https://account.microsoft.com/devices/recoverykey
If the key was saved there, you should be able to unlock your PC.
If you used a work or school account, you may need to contact your organization’s IT administrator.
Unfortunately, if the recovery key is not available, it won’t be possible to access the system because of BitLocker encryption. In this case, the only option is to format the hard drive and reinstall Windows.