How Exactly to add value?

Im making a game that if you click the UI button, your max health will increase + 1, but how can i add it?

i tried

local button = script.Parent
local player = game.Players.LocalPlayer
local char = player.Character

button.MouseButton1Click:Connect(function(plr)
    char.Humanoid.MaxHealth + 1
end)

But doesnt work, im new at scripting so i barely know anythin