The main mistake is to use a public GUI instead of the player's GUI. the path to the local GUI is accessible via game.Players.LocalPlayer.PlayerGUI

local gui = game.Players.LocalPlayer.PlayerGui
local button = gui. -- Enter your path to button

button.MouseButton1Click:Connect(function()
    button.Text = "Clicked"
    wait(1)
    button.text = "CLICK ME"
end)