How can I connect a countdown GUI to a script in the workspace?

So say I have a basic countdown script within a GUI

function countDown()
local Time = script.Parent
for i = 30, 0, -1 do
Time.Text = i 
wait(1)
end
end

So I've tried to make it into a global function, and it works in test mode, however it doesn't work in a server. I've been told you can only use global functions within the same client. So then how would I connect this to a script in the workspace?