How do i stop a function from working?

So my initial thought was using return but it only stops the if question (I think, not sure), not the function itself.

here is a part of my code that i'm having trouble with.

		Progress:GetPropertyChangedSignal("Value"):Connect(function() -- whenever progress changes
			if Progress.Value >= MaxProgress.Value then -- check if progress already reached the max progress cap required to finish
				PLN.Value = PLN.Value + goldreward.Value -- rewarding
				XP.Value = XP.Value + xpreward.Value
				plr.leaderstats.QuestsDone.Value = plr.leaderstats.QuestsDone.Value + 1 -- adding one quest to quests done
				print(plr.leaderstats.QuestsDone.Value + 1, plr.leaderstats.QuestsDone.Value)
				-- clearing the values
				xpreward.Value = 0
				goldreward.Value = 0
				Progress.Value = 0
				QuestID.Value = ""
				MaxProgress.Value = 0
				gui.Title.Text = texttitle
				gui.Subtitle.Text = textsubtitle
				return
			end
		end)

When i call this function again it just doubles the outcome, I deducted it's because the function didn't stop in the first place.

The :Connect function returns a connection that you can call :Disconnect from to stop the function from firing in the future. However, the best use of Connect is to call it once per thing that's going to be changing, not every time you change it. If you're able to run the code every time you change the value, you should simply remove the part where you make a connection and simply run the function yourself.

If you need this to be a connection because other code can change the progress, you may want to store the connections in a table, like this:

-- Top of the script
local connections = {}

-- In your code
connections[plr] = Progress:GetPropertyChangedSignal("Value"):Connect(function()
	-- etc
end)

game.Players.PlayerRemoving:Connect(function(plr)
	connections[plr]:Disconnect()
	connections[plr] = nil
	-- Saving code and other cleanup could go here
end)