Hello
I wish I could share good news, but the truth is no one can get you the bitlocker key, including Microsoft staff/support.
In case the key might be stored somewhere else,
If your friend has set it up with school or work account, it is worth checking here as well https://aka.ms/aadrecoverykey sign in with your work/school email credential in that case.
Otherwise, there's really no way to crack it. Bitlocker means business. If it can be cracked, then it means the encryption is not working. Your only option is to do a clean install of Windows. In that case, you do lose your files. I am very sorry. I hate to share this kind of information, but I rather give you the correct info.