If I get message your iPhone has been hacked what should I do ?

It's a scam, depending on how you receive it you will find a solution in the article linked below.

Take a look at this article:

Recognize and avoid phishing messages, phony support calls, and other scams - Apple Support

If you have any questions just ask!

Good luck!

It would be helpful if you explained where you got the message, but even without knowing exactly where you got it, I would venture to say that it is SCAM.

Ignore it. But, if you provide information as to where you are seeing the message, we can advise further.