Bismillahir Rahmaanir Raheem
Al Jawaab Billahit-Tawfeeq

Respected brother,

If someone praying witr forgets the Qunut and then remembers it while bowing, or
after having risen up from it, then he neither recites it in the ruku nor
returns to the original standing position in order to do so. Rather, he completes
the prayer and performs the Sujud-al-sahw for having missed a mandatory
requisite of the prayer(recitation of the qunut)

If however one utters the Qunut after raising his head from ruku,he is not to
repeat the ruku ,but must perform the sujud al-sahw for moving the qunut from
its original position and delaying a necessary action.
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References:

Radd-Al-Muhtaar- DKI print, Volume 2 pg 446-447
Hashiyat al-Tahtawi- Pg 385, DKI print
Fatawa-Rahimiyyah- Volume 5, pg 230, Darul-Ishaat print



And Allah knows best