Having trouble creating a healing animation?

Hello everyone! I am new to scripting, and I've tried to create a potion script. Basically, if your health is below 50, you can press a certain key to heal yourself. The problem is that I don't know how to create one, so I've tried doing this:

local player = game.Players.LocalPlayer
local mouse = player:GetMouse()
local animation = Instance.new("Animation")
animation.AnimationId = "assetidhere"
local character = player.Character
local humanoid = game.Players.LocalPlayer.Character.Humanoid
local animationHealth = 50


if player.character.humanoid.Health > 50 then
humanoid.animationHealth:connect(function(health)
    local change = math.abs(currentHealth + animationHealth)

mouse.KeyDown:connect(function(key)
    if key == "h" then 
        animation.Play()
        wait (5)
        animation.Stop()


end)

Could someone please tell me how I would do something like this, as I can't get it to work? Thank you for your time. I purposely removed the asset id, so that is not the problem. Again, thanks you for your time.