assuming you are an average weight adult you don't have to do anything. adults can take 600 mg to a maximum of 800 mg every 8 hours. you only took 400 mg and then took 400 mg more seven hours later. you will be fine.
accidently took more advil. i took 2 advil earlier around 7 or 8 and i forgot and took 2 more just now at 2am. what do i do?