How can I change the image of an ImageLabel when a player's health goes down?

How do I change the image of an ImageLabel when the player's health goes below a specific level? I've tried to look up many tutorials and tried my own script but none of them work. Can I have a bit of help?

For example, I have an image that is green, indicating the player's health is at the max. But when it goes below a specific level, the image changes. However, there are two more specific places of health the player reaches to change the image again.

Can someone help me? (Sorry if it doesn't make any sense)

This is a script I found from a tutorial but it doesn't work.

repeat wait() until game:GetService("Players").LocalPlayer
local Character = workspace:FindFirstChild(game.Players.LocalPlayer.Name)

while wait() do
	if Character:FindFirstChild("Humanoid") then	
		if Character.Humanoid.Health.Value >= 75 then
			script.Parent.ScreenGui.ImageLabel.Image = "rbxassetid://6105945560"
		end
	end
end