Sayyed Muhammad Husaini Ragheb, Sayyed Muhammad Husaini Ragheb has a BA in Law from Guilan University, Iran and has also undertaken Hawzah studies in Qom. He is a Cultural Affairs director of Ethics Group of Al-Mustafa Open... Answer updated 10 months ago

In Rokou' when you bend down it is enough to repeat سُبْحانَ اللّهِ  (i.e. subḥānal lāh ) three times or say سُبْحانَ رَبِّیَ الْعَظیمِ وَبِحَمْدِهِ (i.e. subḥāna rabbiyal ʿaẓīmi wa biḥamdih ) only once.

If you didn't know the ruling and just bowed down you don't need to repeat those prayers.