how do i make it so it only rewards the client that killed the npc?

so like its rewarding all clients and i dont want that how do i fix this???

local rep = game.ReplicatedStorage
local remote = rep:WaitForChild("ChangeValue")

debounce = true

while true do
	wait(1)
local plr = game:GetService("Players").LocalPlayer
local Gui = plr.PlayerGui.Quest:WaitForChild("DOIT")
local Gui1 = plr.PlayerGui.Quest:WaitForChild("Framo")
local Humanoid = game.Workspace.ThiefBoss:FindFirstChild("Enemy")

Humanoid.Touched:Connect(function(hit)
	local hum = hit.Parent:FindFirstChild("Humanoid")
	if Humanoid ~= nil and debounce == true then
		debounce = false
		game.Players:GetPlayerFromCharacter(hit.Parent)
		Humanoid.Died:Connect(function()
			if hit.Parent then
		    Gui:TweenSize(UDim2.new(0,227,0,152), Enum.EasingDirection.In, Enum.EasingStyle.Elastic,1,true,nil)
	        wait(1)
	        Gui.Visible = false
			if Gui.Visible == false then
			Gui1.TextLabel.Text = "Thank you for defeating the Thief Boss"
	remote:FireServer("Quest")
	wait()
	debounce = true
			end
			end
		end)
		end
	end)
end

You will have to detect who touched the player last so that you know who killed him

This should be in a serverscript and will be something along the lines of

local rep = game.ReplicatedStorage
local remote = rep:WaitForChild("ChangeValue")
local plr = game:GetService("Players").LocalPlayer
local Gui = plr.PlayerGui.Quest:WaitForChild("DOIT")
local Gui1 = plr.PlayerGui.Quest:WaitForChild("Framo")
local Humanoid = game.Workspace.ThiefBoss:FindFirstChild("Enemy")

local lastTouch
Humanoid.Touched:Connect(function(hit)
    local p = game.Players:GetPlayerFromCharacter(hit.Parent)
    if p then
        lastTouch = p
    end    
end)
Humanoid.Died:Connect(function()
    local playerWhoKilled = lastTouch
    --Do stuff here
end)