my father passed away . How I can unlock his Ipad

FYI … NO ONE … not even Apple … can “unlock” the iPad.

It can ONLY be unlocked by correctly entering the passcode. Period.

The best that Apple can do is provide access to the AppleID.

Another possibility …

… did your father possibly establish a Legacy Contact?

If so, it can streamline the process already described in link at Demo’s post.

See:

Request access to an Apple account as a Legacy Contact – Apple Support (AU)

See this for help.

How to request access to a deceased family member's Apple account - Apple Support