Gui giver with lighting?

So...I'm trying to turn this script into a giver that i can use on a Gui Button. But i cant figure out how i can make the Click function work with a gui button?

Script Below...

local itemname = "Ggs"

local item = game.Lighting:findFirstChild(tostring(itemname))

local trigger = script.Parent

enabled = true

function onClick(plyr)

	if plyr.Backpack:findFirstChild(tostring(itemname)) == nil and enabled == true then

		enabled = false

		trigger.BrickColor = BrickColor.new("Black")

		local itemclone = item:clone()
		itemclone.Parent = plyr.Backpack
		
		wait(2)

		enabled = true
		trigger.BrickColor = BrickColor.new("Bright blue")

	end
end

script.Parent.ClickDetector.MouseClick:connect(onClick)

Sorry if I'm wrong, but the local variables have to be declared inside the function. Here is the new code:

enabled = true

function onClick(plyr)

if plyr.Backpack:findFirstChild(tostring(itemname)) == nil and enabled == true then

local itemname = "Ggs"

local item = game.Lighting:findFirstChild(tostring(itemname))

local trigger = script.Parent

enabled = false

        trigger.BrickColor = BrickColor.new("Black")

        local itemclone = item:clone()
        itemclone.Parent = plyr.Backpack

        wait(2)

        enabled = true
        trigger.BrickColor = BrickColor.new("Bright blue")

    end
end

script.Parent.ClickDetector.MouseClick:connect(onClick)

But wait! You haven't declared what "plyr" is. I would do this: (THIS SCIPT MUST BE A LOCALSCRIPT FOR IT TO WORK!!!) Oh, and remove "plyr" from the parentheses from the function.

local plyr = LocalPlayer
local Backpack = plyr:WaitForChild("Backpack")
-- Put this with all your local variables

Also, why are you using

tostring
~~~~~~~~~~~~~~~~~ ?

You don't have to change much, other than plyr.Backpack and put it in a "LocalScript". Here is the GUI Version:

local itemname = "Ggs" 

local item = game.Lighting:findFirstChild(tostring(itemname)) 

local trigger = script.Parent

local enabled = true

-- function onClick(plyr)  This would be declared as the mouse instead of the player.
 function onClick()
local plyr = game.Players.LocalPlayer -- This is a way of getting the 'Player' (In the 'Players' Section of game)
    if plyr.Backpack:findFirstChild(tostring(itemname)) == nil and enabled == true then

        enabled = false

        trigger.BackgroundColor3 = Color3.new(0,0,0) -- Changes the background to BLACK. You might want to also change the text color, if you are using a textbutton for this.

        local itemclone = item:Clone()
        itemclone.Parent = plyr.Backpack

        wait(2)
 trigger.BackgroundColor3 = Color3.new(0,0,255) -- Changes the background to BLUE.
        enabled = true
       
    end
end

script.Parent.MouseButton1Down:connect(onClick) --[[This is the LEFT button of your mouse. If the player pushes down the left mouse button, it will fire.]]--