What should a person do if they forget to perform the prostration of forgetfulness (sujood as-sahw)?

If a person forgets or mistakenly omits the required prostration of forgetfulness (sujood as-sahw), and after saying the salam engages in an act that invalidates the prayer—such as laughing, speaking, or turning away from the qibla—or if there is no longer time to perform the prostration, then the obligation of sujood as-sahw is lifted from that person. It is not necessary to repeat the prayer. However, if the person remembers the prostration before doing anything that invalidates the prayer, they should perform the prostration immediately (Kâsânî, Bedâi‘, 1/174).

Source: T.C. Diyanet İşleri Başkanlığı, Din İşleri Yüksek Kurulu