iCloud Lock. Activation Code!

Hello lovely People. Hope you all are doing great! I wanted a small help regarding the iCloud lock on behalf of my Dad.

My Dad had bought an iPhone X 256GB and he had created an Apple ID. Now he has forgotten the ID. Even he cannot remember any single thing which he entered while creating. Now the phone is Locked and asks for Activation Code.

what can I do in this regard? Is there anyway this can be unlocked?? I saw many posts and videos but i was not sure about those at all and I came here to seek help. How could I do this authentically without any spam or fake attempts? Please be kind enough and share your experience if u had done it before and succeeded...

thanks aloot and have a great day !