Stopping Prompt Message After One Time

I have some columns that auto unhide and when this happens, a prompt message displays to inform the user to complete the next level.

However, whenever the user makes another selection, the prompt box keeps coming back up.

How would I only run the message once?

This is the code I am using and I have attached the sheet,

Private Sub Worksheet_Change(ByVal Target As Range)
    Columns("C:D").EntireColumn.Hidden = Range("B49").Value < 3
    
    Columns("E:F").EntireColumn.Hidden = Range("D49").Value < 3
    
    If Range("D49").Value = 3 Then
    MsgBox "Please complete assessment for Mastery Level"
    
    ElseIf Range("B49").Value = 3 Then
    MsgBox "Please complete assessment for Intermediate Level"

    End If
    
        
End Sub

Try this...I think i understand what you are after. Basically, change the order of the operations (prompt then unhide) then you can use and IF statement to only perform the action IF the columns are hidden.

That way, once they are not hidden, the message will not fire again.

Private Sub Worksheet_Change(ByVal Target As Range)
    
    If Columns("E:F").EntireColumn.Hidden = True Then
        If Range("D49").Value = 3 Then
            MsgBox "Please complete assessment for Mastery Level"
            Columns("E:F").EntireColumn.Hidden = Range("D49").Value < 3
        End If
    End If
    If Columns("C:D").EntireColumn.Hidden = True Then
        If Range("B49").Value = 3 Then
            MsgBox "Please complete assessment for Intermediate Level"
            Columns("C:D").EntireColumn.Hidden = Range("B49").Value < 3
        End If
    End If
    
End Sub

But, i wasn't sure if this made the sheet function exactly how you want, it does handle the "don't prompt again" part of things