What should I do if, while bowing in the second rak'ah, I remember that I forgot to bow in the first rak'ah?

If someone forgets the bowing (ruku‘) of the first rak‘ah and remembers it while bowing in the second rak‘ah, then the first rak‘ah is annulled, and the rak‘ah in which he is currently bowing becomes the first rak‘ah. He then completes his prayer and performs the prostrations of forgetfulness (sujud al-sahw), because rectifying the forgotten bowing becomes impossible once he bows for the subsequent rak‘ah. This is the relied-upon position in the Maliki school of thought.