" 12 is not a valid member of IntValue" ?

idk what to do

local Dad = game.ServerStorage.PlayerData:WaitForChild("Dadithan", 20)
local F = Dad.Inventory


function si()
	if F["12"].Value == 1 then
		F["12"].Value = 100
		F["12"].Metal.Value = 14
		F["12"].Wood.Value = 15	
		F["12"].Name = "40"
	end
end

si()

Create an instance of IntValue:

local i = Instance.new("IntValue")

Then apply it to your script.