I have the code correct, but am unsure of how to implement it?

Thanks to perci1 I understand a little more of what I need to do.

This is my previous code:

game.PlayerGui.GUI1.Visible = false
wait(4)
game.PlayerGui.GUI2.Visible = false

He has informed me that the CORRECT code would be this:

script.Parent.GUI1.Visible = false
wait(4)
script.Parent.GUI2.Visible = true

So now, I know the correct code.

But I am unsure of how to implement it. I put it under where the brick disappear code is, meaning it's like this:

function cover()
    print("Holding Cell")
    game.Workspace.checkpoint1.Transparency = 1
    script.Parent.GUI1.Visible = false
end

checkpoint1.Touched:connect(cover)

IT'S STILL NOT WORKING.

Why won't the GUI disable with the brick!? The code is supposed to make both go away but it wont' work.