Is anything required of the congregants who prostrated, assuming the Imam had prostrated?

Those led in prayer (ma'mumin) who prostrated out of forgetfulness, thinking that the Imam prostrated for a recitation (sujud at-tilawah), must rise from prostration, then bow, and then follow their Imam. They are excused for their forgetfulness. Sheikh Ibn Uthaymeen mentioned that this delay due to an excuse is permissible and does not necessitate the prostration of forgetfulness (sujud as-sahw).

Some jurists are of the opinion that they should not stand upright, but rather rise only to the extent of bowing, say the glorifications of bowing, then rise from bowing and follow the Imam. This is because if they were to stand upright and then bow, their prayer would be invalidated due to the addition of another bowing.