How do I find the text of a TextBox using a RemoteEvent?

This might be a little confusing, sorry! :|

I don't know how to find an object in a GUI using a script in ServerScriptService.

(This is an admin panel that only allows specific players access, which makes this harder for me)

The script does an OnServerEvent, so that when the button fires the event, it does the specific code and supports FilteringEnabled.

Here's my code:

game.ReplicatedStorage.ChatMakeMessage.OnServerEvent:Connect(function(player)
    print("System message event was fired!")
    bc = BrickColor.new("Institutional white")
    game.StarterGui:SetCore("ChatMakeSystemMessage", {
        Text = player.PlayerGui:WaitForChild("Administration").ActualPanel.messageBox.Text;
        Font = Enum.Font.GothamBold;
        Color = bc.Color;  
    })
end)

I've tried doing game.StarterGui.Administration as well, Nothing works