another roblox script inside of you when you join, and its the health script

-- Gradually regenerates the Humanoid's Health over time.

local REGEN_RATE = 1/100 -- Regenerate this fraction of MaxHealth per second.
local REGEN_STEP = 1 -- Wait this long between each regeneration step.

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local Character = script.Parent
local Humanoid = Character:WaitForChild'Humanoid'

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while true do
    while Humanoid.Health < Humanoid.MaxHealth do
        local dt = wait(REGEN_STEP)
        local dh = dt*REGEN_RATE*Humanoid.MaxHealth
        Humanoid.Health = math.min(Humanoid.Health + dh, Humanoid.MaxHealth)
    end
    Humanoid.HealthChanged:Wait()
end