Answered by: Maulana Imran Mughal
How does one perform sajda sahwa?
بِسْمِ اللهِ الرَّحْمنِ الرَّحِيْم
In the name of Allah, the Most Gracious, the Most Merciful.
Sajdah Sahw is performed in the following manner:
In the last rakah of salah the person should recite At-Tahiyyat only and thereafter make salam towards the right only, then he should make two sajdahs. After that, he should recite At-Tahiyyat again and thereafter recite the durud, dua and salam to both sides completing his salah. 
And Allah SWT alone knows best.
Written by Maulana Imran Mughal
Checked and approved Mufti Mohammed Tosir Miah
Darul Ifta Birmingham
Mawlana Ashraf Ali Tahanwi, BahishtiZewar(Karachi: Maktabat Bayt al-ilm, 2007), 182.
This answer was collected from DarulIftaBirmingham.co.uk, which is run under the supervision of Mufti Mohammed Tosir Miah from the United Kingdom.