while true do game.Workspace.Player.Humanoid.Health=100 wait(3) game.Workspace.Player.Humanoid.Health=98 wait(3) game.Workspace.Player.Humanoid.Health=96 wait(3) game.Workspace.Player.Humanoid.Health=94 wait(3) game.Workspace.Player.Humanoid.Health=92 wait(3) game.Workspace.Player.Humanoid.Health=90 wait(3) game.Workspace.Player.Humanoid.Health=88 wait(3) game.Workspace.Player.Humanoid.Health=86 wait(3) game.Workspace.Player.Humanoid.Health=84 wait(3) game.Workspace.Player.Humanoid.Health=82 wait(3) game.Workspace.Player.Humanoid.Health=80 wait(3) game.Workspace.Player.Humanoid.Health=78 wait(3) game.Workspace.Player.Humanoid.Health=76 wait(3) game.Workspace.Player.Humanoid.Health=74 wait(3) game.Workspace.Player.Humanoid.Health=72 wait(3) game.Workspace.Player.Humanoid.Health=70 wait(3) game.Workspace.Player.Humanoid.Health=68 wait(3) game.Workspace.Player.Humanoid.Health=66 wait(3) game.Workspace.Player.Humanoid.Health=64 wait(3) game.Workspace.Player.Humanoid.Health=62 wait(3) game.Workspace.Player.Humanoid.Health=60 wait(3) game.Workspace.Player.Humanoid.Health=50 wait(3) game.Workspace.Player.Humanoid.Health=42 wait(3) game.Workspace.Player.Humanoid.Health=40 wait(3) game.Workspace.Player.Humanoid.Health=32 wait(3) game.Workspace.Player.Humanoid.Health=30 wait(3) game.Workspace.Player.Humanoid.Health=22 wait(3) game.Workspace.Player.Humanoid.Health=20 wait(3) game.Workspace.Player.Humanoid.Health=12 wait(3) game.Workspace.Player.Humanoid.Health=10 wait(3) game.Workspace.Player.Humanoid.Health=0 end
If you want to make this run online, you should put it in a local script, put the script in the player and replace game.Workspace.Player to game.Players.LocalPlayer.Character
Also, Loops are helpful.
for i = game.Players.LocalPlayer.Character.Humanoid.Health, 0, -2 do game.Players.LocalPlayer.Character.Humanoid.Health = i wait(3) end