Why does my tool not change a value within a part after colliding with it?

I think the problem here is, you are looking for a child named “NumberValue” but not a NumberValue itself.

Use FindFirstChildWhichIsA() to find a type of child instead of the name of a child

Properties = {
    debounce = true, -- Leave this on true.
    sound_fx = true, -- If you don't want sound to play when tool is activated set this to false.
    anim_check = true, -- If you don't want animation to play when tool is activated set this to false.
    ToolDrop = false, -- Set this to true if you want to be able to drop the tool by pressing BackSpace.
    soundID = 6042531284, -- Sound Id.
    AnimID = 6461572129, -- Your Animtion id.
    debounce_lenght = 1, -- how long it will take before you can click again, aka cooldown so you can't spam click the tool.
    soundDelay = 0.25, -- How long to wait before playing sound
    enableTrail = true, -- Enable trail thing
    trail = script.Parent.Head.Trail, -- the trail thing
    damage = 5 -- how much dmg the thing does
}

local Tool = script.Parent
local Handle = Tool:WaitForChild("Handle")
local BaseUrl = "rbxassetid://"
local anim = Tool:WaitForChild("Animation")
local Players = game:GetService("Players")


if Properties.sound_fx then 
    sound = Handle:WaitForChild("Sound")
    sound.SoundId = BaseUrl .. Properties.soundID
    sound.MaxDistance = 100
    sound.RollOffMode = Enum.RollOffMode.InverseTapered
end



if Properties.anim_check then   
    anim.AnimationId = BaseUrl .. Properties.AnimID
end


if Properties.ToolDrop == true then
    Tool.CanBeDropped = true
end

Tool.Equipped:Connect(function(Mouse) -- When you equip the tool
    local player = Players:GetPlayerFromCharacter(Tool.Parent) -- gets the player
    if Properties.anim_check == true then animation = player.Character.Humanoid:LoadAnimation(anim)end -- loads animation

    Tool.Activated:Connect(function() -- when you click with the tool
        if Properties.debounce then
            Properties.debounce = false
            if Properties.anim_check == true then animation:Play()end
            if Properties.sound_fx == true then wait(Properties.soundDelay) sound:Play()end

            if Properties.enableTrail == true then
                Properties.trail.Enabled = true
                wait(0.2)
                Properties.trail.Enabled = false
            end

            script.Parent.Head.Touched:Connect(function(Hit)
                print(Hit.Name)
                if Hit:FindFirstChildWhichIsA("NumberValue") and Hit:FindFirstChildWhichIsA("NumberValue").Name == "Health" then
                    local temp = Hit:FindFirstChildWhichIsA("NumberValue")
                    print(temp.Name .. ": " .. temp.Value)
                    temp.Value = temp.Value - Properties.damage
                end
            end)

            wait(Properties.debounce_lenght)    
            Properties.debounce = true
        end 
    end)
end)
Tool.Unequipped:Connect(function()
    if Properties.anim_check == true then animation:Stop()end
    if Properties.sound_fx then sound:Stop()end
end)