How to add a damage script on this function?

This is how you damage people, i do not understand fully what you want, but this is my best trying to understand what you want, this will also not replicate to the server meaning nobody else including the target player will see the damage occur to them. I suggest remote events for doing that

Use this:

local mouse = game.Players.LocalPlayer:GetMouse()
local canDamage = false
local damageAmount = 20 -- modify this to whatever you want

script.Parent.Equipped:Connect(function()
    local Wield = game.Players.LocalPlayer.Character.Humanoid:LoadAnimation(script.Wield)
    Wield:Play()

    mouse.Button1Down:Connect(function()
        local Wield = game.Players.LocalPlayer.Character.Humanoid:LoadAnimation(script.Wield)
        local Attack = game.Players.LocalPlayer.Character.Humanoid:LoadAnimation(script.Attack)
        Wield:Stop()
        Attack:Play()
    end)

    mouse.Button1Up:Connect(function(hit)
        local target = mouse.Target
	
	if target.Parent:FindFirstChild("Humanoid") then
		local charTarget = target.Parent

		charTarget.Humanoid:TakeDamage(damageAmount)
	end
    end)

end)