How do I make a humanoid sit when on low health? Im a beginner

So, im making a script so when someone is shot and are at a certain amout of health they are downed meaning they fall and cannot move or switch tools in their backpack. It also will show a small message that isn't covering their screen that says you have been downed which goes away in a few seconds. I can't seem to understand how to start or make a script like this, if anyone can help me that would be great.

--Make a check when the health is changed, if health is <= the min value then sit

--StarterPlayer > StarterCharacterScripts
-- I hope this works 

local plr = game.Players.LocalPlayer

repeat wait()
	
until plr.Character
wait()
local char = plr.Character

char.Humanoid.Changed:connect(function()
	if char.Humanoid.Health <= 50 then -- Change 50 to your value
		char.Humanoid.Sit = true
		
	else
		--Optional
		-- char.Humanoid.Sit = false 
		print(char.Humanoid.Health)
	end
end)