Is the prayer led by an Imam who made a mistake in a verse then corrected it after being prompted by the congregant valid or invalid, and should the prayer be repeated?

The prayer is valid and does not need to be repeated, because the Imam said "yes" out of ignorance of the ruling on speaking during prayer or due to forgetfulness. This does not affect the validity of the prayer if it is minor. Mu'awiyah ibn al-Hakam said "May Allah have mercy on you" to someone who sneezed during prayer, and the Prophet, peace be upon him, did not order him to repeat it.