How would I change health from unequiping a tool?

script.Parent.Equipped:Connect(function()
	local Humanoid = script.Parent.Parent.Humanoid
	script.Parent.Parent.Humanoid.MaxHealth = 200
	script.Parent.Parent.Humanoid.Health = 200
end)
script.Parent.Unequipped:Connect(function()
	local Humanoid = script.Parent.Parent.Humanoid
	script.Parent.Parent.Humanoid.MaxHealth = 100
	script.Parent.Parent.Humanoid.Health = 100
end)

When I un-equip it, it thinks that I mean the Player.Backpack, but I want to get the humanoid. It works for the first one

Hello,

The reason you are encountering this issue is because when a tool is equipped, it is placed within the player's character. When a tool is unequipped, it is placed within the player's backpack.

Because you did not use code blocks or format your original post, I've taken the time to format your original code:

script.Parent.Equipped:Connect(function() 
	local Humanoid = script.Parent.Parent.Humanoid 
	script.Parent.Parent.Humanoid.MaxHealth = 200 
	script.Parent.Parent.Humanoid.Health = 200 
end) 

script.Parent.Unequipped:Connect(function() 
	local Humanoid = script.Parent.Parent.Humanoid 
	script.Parent.Parent.Humanoid.MaxHealth = 100 
	script.Parent.Parent.Humanoid.Health = 100 
end) 

We can see in your code, that when the Unequipped function is called you attempt to set the humanoid variable as the tool's parent... Which is the player's backpack.

To fix this issue, there are a few things I would recommend:

Assign the Localplayer's player object, character, and humanoid at runtime. This way you don't need to keep assigning the player's humanoid every time you pull in/out the weapon. To do this we would add the following to your code:

local Player = game:GetService("Players").LocalPlayer --assign local player

workspace:WaitForChild(Player.Name) --wait for local player's character to be loaded

local Character = Player.Character -- assign player's character
local Humanoid = Character.Humanoid --assign humanoid from character

script.Parent.Equipped:Connect(function() 
	Humanoid.MaxHealth = 200 --change function to use new variable
	Humanoid.Health = 200 
end) 

script.Parent.Unequipped:Connect(function() 
	Humanoid.MaxHealth = 100 --change function to use new variable
	Humanoid.Health = 100 
end) 

This solution fixes your issue by making sure the humanoid is referenced properly AND allows you to clean up your code.

Hope this answer helped you!

Cheers,

Chase