In case a person makes a mistake or thinks that he has made a mistake in the utterances and practices of the prayer fixed in Sharia, the amendment prescribed as a sunnah is that if amends can be made for the mistake, then they should be made and two prostrations (called “prostrations in lieu of a mistake”) should be offered before ending the prayer or after ending the prayer (both methods are acceptable); and if making amends is not possible, then only the prostrations should be offered.

Sajda-e-Sehav can be done at a later point even after the prayer, as soon as one remembers that they were supposed to perform it.

Please refer to the videos provided in the following thread to understand the underlying concept of Sajda-e-Sehaw:

Discussion 48559

Please refer to the following portion of Ghamidi Sahab’s book Meezan where all narrations regarding Sajda-e-Sahaw have been collected in one place and from these narrations, you’ll be able to see the application of Sajda-e-Sehaw principle with much clarity:

https://www.javedahmedghamidi.org/#!/mizan/5aa6a4315e891e8f44a45788?chapterNo=4&subChapterNo=0&subChsecNo=9&lang=en