When this game.StarterGui.ScreenGui.TimerTime.Value script is executed, its value changes every second (as it should be), game.StarterGui.ScreenGui.Frame.ManyPlayers.Text also changes, but it constantly writes one number on the game screen.
while game.StarterGui.ScreenGui.GameStarted.Value == true do
game.StarterGui.ScreenGui.Frame.TextLabel.Text = "WAIT"
game.StarterGui.ScreenGui.Frame.ManyPlayers.Text = "00:" .. game.StarterGui.ScreenGui.TimerTime.Value
wait(1)
game.StarterGui.ScreenGui.TimerTime.Value = game.StarterGui.ScreenGui.TimerTime.Value - 1
end

1 comment
You need to access the players gui not the starter gui