One of my Client's Facebook Account is Locked & asking for Date of Birth which I don't remember now.

Ask your client for his or her DOB.

Failing that, https://www.facebook.com/help/community/question/?id=1149835008376621

Client or not, what business do you have attempting to manipulate someone else's account. Ask your client to solve this problem, Alisha/Jvion Health.

In all fairness, I've been given the keys to clients' accounts (technically, they are not supposed to do that). But never Facebook, as it's a private account. Clients should have pages or groups, and the administration of those can be made by anyone with a valid FB account given access to do so.

I don't remember the DOB used to create this account. Is there any other way to unlock the account?

Client can't help in this as we have created this account. Is there any other way to unlock this account.

Probably not, seeing as it's a fake DOB. If it isn't a lot of followers, drop it and move onto making another account. And keep better records of that one.