How to make my script only if work if the tools aren't in the person inventory?

function hi(x)
local y = x.Backpack
local z = game.Lighting["Dragon Slayer"]
z:Clone().Parent = y -- then put your item in lightning.
end

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

So this is my code above... how would I fix this so that if the tool that is being given is already in the person inventory not be given otherwise if they don't have the tool it will be given?

function hi(Plr)
local Lighting = game:GetService("Lighting")
local Backpack = Plr.Backpack
local DS = Lighting["Dragon Slayer"]:Clone()
DS.Parent = Backpack
end

script.Parent.ClickDetector.MouseClick:Connect(hi(Player))

You should use "if statements"

local  z =  game.Lighting["Dragon Slayer"]
if x.BackPack:FindFirstChild(z) then
print("has")
end
else z:Clone().Parent =  x.BackPack
end