Wa alaikum al-salaam wa rahmatullahi wa barakatuh
It is recommended for the masbūq to read the sūrah along with the fātiha in the first two rakʿah(s) if one is able to do so, otherwise it is recommended for him to read the sūrah along with the fātiha in the two rakʿah(s) that he prays after his imam does the taslīm. However, it is not recommended to read them out loud.
Allah knows best.
Answered by: Shaykh Omar Mohsin