textlabel and wait() problem can somebody please help me?

so basically im trying to make a script and it seems that whenever i do wait(number) before it it doesnt do anything heres the script

wait(3)

game.StarterGui.ScreenGui.TextLabel.Text = "test"

StarterGui is a placeholder for Guis. Content inside StarterGui get replicated to the Local Player's PlayerGui. The Gui itself is in the PlayerGui. Here is the Local Script:

local plr = game:GetService("Players").LocalPlayer
wait(3)
plr:WaitForChild("PlayerGui").ScreenGui.TextLabel.Text = "Test"