Hi Neha,
If you do not have the bitlocker key to unlock it you can:
Finding your BitLocker recovery key in Windows
https://support.microsoft.com/en-us/windows/finding-your-bitlocker-recovery-key-in-windows-6b71ad27-0b89-ea08-f143-056f5ab347d6
If it does not appear there you will need to wipe your device with a new Windows 10 image:
Create Windows 10 installation media
https://www.microsoft.com/en-ca/software-download/windows10
If this is helpful please accept answer.