All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
An individual who forgot to recite Al-Faatihah and then recited it before the Rukoo‘ is not obliged to do anything. However, he has to recite some portion of the Quran after it since the portion he recited before it did not meet its proper position.
Allaah Knows best.