All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
It is recommended for him to recite out loud in one of the two Rak‘ahs he makes up, being the second in order in such a case, and then to recite in a low tone in the following one.
The questioner must pay attention that he is permitted to recite out loud if he causes no confusion or noise to others who are offering prayers around him whether they are obligatory or voluntary prayers. Therefore, if he fears that he will cause confusion to others around him, then he must recite in a low tone.
Allaah Knows best.