Question:

I was wondering what do I have to do if I did an extra rakah or missed one because I didn’t complete a sujood? If you could explain it to me as simply as possible so that I understand I would be so grateful and may Allah reward you to your kindness.

Answer:

All praise is due to Allah.

It is very nice to hear from you.

If a person adds an extra rakah forgetfully, they should make two
prostrations after saying salam once on the right, then make their
regular salaams.

That is, they sit down and finish their tashaahud, then say salam once
on the right, then make two prostrations of forgetfulness, then do
the salam again on the right and left.

If a person missed a sajdah then they must repeat the entire rakaah,
and then do two prostrations of forgetfulness before giving salam.
That is they finish their tashaahud, then make two sajdahs of
forgetfulness, then give salam once on the right and left.

In other words, if you add something to the prayer, you should say
salam first, then make the sajdahs, then make the salaam on the right
and left.

If you subtract something from the prayer, like leaving out a sajdah,
you repeat the rakah then make two sajdahs of forgetfulness before
giving the salams. In this case, you only give salams once.

There are some differences of opinion amongst the madhahab, but this is the view that seems to be supported by the evidence.

Allah knows best.