What is the default restriction code for iPhone 7plus ..i hv no idea?pls advise

There is no such thing as a default restrictions passcode.

The restrictions passcode can only be set by one of 2 methods.

A person actually entering it twice to confirm it, or a corporate profile installed generally with an Exchange email account.

If you do not know, the passcode, and the iPhone is not a corporate phone, then the only way to remove it is to restore the iPhone.