sorry you do not have sufficient permissions notification

Hello,

How do I block this notification from non admins (or everyone, Im not too bothered which, as long as the message can be blocked) who are accessing pages at the back end? My customers keep seeing your notices, which isnt good and contacting me about it. I have seen 4 aspects of them residing in functions.php. I have a child theme but would like to know exactly how to completely remove these notifications with a snippet I can add to the child theme. Please be code specific

Many thanks.