How to change every player's gui all at once?

I need to get all players' output textboxes and change the texts all at once. I am doing this from a normal script in workspace.

I tried here by creating a variable:

O = game.Players:GetChildren()
output = O.PlayerGui.GameGui.Output.TextLabel

I was told that I need to do this locally, but I need this in the same script as the other stuff.

Help me fix this. Thanks.

Replace that with this:

local plrs=game.Players:GetPlayers()
for i=1,#plrs do
	output=plrs[i].PlayerGui.GameGui.Output.TextLabel
end

Have a remote event connect the client and catch changes from the remote event. Then use FireAllClients on the remote event from the server and change the gui on every client <- Should be near simultaneous.