How to add EXP into a OnKeyPressed script?

I have been trying to use an EXP script that I have but the problem was I couldn't add it to my existing tool so that every time the tool is used, it would give the person who used it EXP. This is the main script to gain EXP when a NPC is "killed":

function onHealthChanged() 
	local zHuman =  script.Parent:findFirstChild( "Humanoid" )
	if zHuman ~= nil then 
		local tag = zHuman:findFirstChild( "creator" ) 
		if tag ~= nil then 
			if tag.Value ~= nil then 
				local stats = tag.Value:findFirstChild("supercool") 
				if stats ~= nil then 
					if tag.Value.Character ~= nil then 
						stats.XP.Value = stats.XP.Value + 20 -- Edit for a custom amount of XP added
					end
				end
			end 
		end 
	end
	
end 

I just need help in how to put this into any of my scripts, but mainly this part of my script:

if key == "z" then
    Deduction = 49.1
    if Player.Chakra.Value >= Deduction then
        Player.Chakra.Value = Player.Chakra.Value - Deduction
        game:GetService("Chat"):Chat(Player.Character.Head, "Flying Thunder God Technique")
        RightShoulder = Player.Character.Torso["Right Shoulder"]
        LeftShoulder =  Player.Character.Torso["Left Shoulder"]
        for i = 1, 2 do
            RightShoulder.C0 = RightShoulder.C0 * CFrame.Angles(0, 0.8, 0)
            wait()
        end
        x = game.Lighting.FlashKunai:clone()
        x.Parent = game.Workspace
        x.CFrame = Player.Character.Torso.CFrame * CFrame.new(0, 0, -1)
        x.Name = Player.Character.Name
        if Tool.Special.Value == 0 then
            x.Slash.Disabled = false
        elseif Tool.Special.Value == 1 then
            x.Slash2.Disabled = false
        end
        Path = Instance.new("BodyVelocity")
        Path.Parent = x
        Path.maxForce = Vector3.new(math.huge, math.huge, math.huge)
        Path.velocity = Player.Character.Torso.CFrame.lookVector * 225
        wait(0.3)
        F = x.Fire:clone()
        F.Parent = Player.Character.Torso
        F.Size = 15
        F.Heat = 25
        F.Enabled = true
        wait(0.1)
        Player.Character:MoveTo(x.Position + Vector3.new(0, 2, 0))
        F:Destroy()
        x:Destroy()
        for i = 1, 2 do
            RightShoulder.C0 = RightShoulder.C0 * CFrame.Angles(0, -0.8, 0)
            wait()
        end
    end
end

Just in case I included the beginning of the script down here for reference: Beginning

enabled = true
function onKeyDown(key) 
if not enabled then return end
enabled = false
local Tool = script.Parent
local Player = game.Players:GetPlayerFromCharacter(script.Parent.Parent)
key = key:lower()

It would be a great help of commenting some ways of adding it or even answering it! Thanks for reading!

I tabbed it for you!

if key == "z" then
	Deduction = 49.1
	if Player.Chakra.Value >= Deduction then
		Player.Chakra.Value = Player.Chakra.Value - Deduction
		game:GetService("Chat"):Chat(Player.Character.Head, "Flying Thunder God Technique")
		RightShoulder = Player.Character.Torso["Right Shoulder"]
		LeftShoulder =  Player.Character.Torso["Left Shoulder"]
		for i = 1, 2 do
			RightShoulder.C0 = RightShoulder.C0 * CFrame.Angles(0, 0.8, 0)
			wait()
		end
		x = game.Lighting.FlashKunai:clone()
		x.Parent = game.Workspace
		x.CFrame = Player.Character.Torso.CFrame * CFrame.new(0, 0, -1)
		x.Name = Player.Character.Name
		if Tool.Special.Value == 0 then
			x.Slash.Disabled = false
		elseif Tool.Special.Value == 1 then
			x.Slash2.Disabled = false
		end
		Path = Instance.new("BodyVelocity")
		Path.Parent = x
		Path.maxForce = Vector3.new(math.huge, math.huge, math.huge)
		Path.velocity = Player.Character.Torso.CFrame.lookVector * 225
		wait(0.3)
		F = x.Fire:clone()
		F.Parent = Player.Character.Torso
		F.Size = 15
		F.Heat = 25
		F.Enabled = true
		wait(0.1)
		Player.Character:MoveTo(x.Position + Vector3.new(0, 2, 0))
		F:Destroy()
		x:Destroy()
		for i = 1, 2 do
			RightShoulder.C0 = RightShoulder.C0 * CFrame.Angles(0, -0.8, 0)
			wait()
		end
	end
end