how to unlock ipad with itunes store

You don’t use the iTunes Store app to unlock the iPad. You have to use the iTunes app on a computer, or the Finder on a Mac if running Catalina or Big Sur.

See this for help.> If you forgot the passcode on your iPad, or your iPad is disabled - Apple Support

If you don't know the password on your iPad, you will have to connect it to your computer and erase it using iTunes (not the iTunes Store), following the directions in this link --> If you forgot the passcode on your iPad, or your iPad is disabled - Apple Support

Can you not ask your brother what he changed the code to?

J