One who has to make up six or more missed salah, he is not asked to maintain order between qadha and in-time prayers, he is at liberty whether to perform qadha first or the in-time prayer first. Both the ways are lawful. But, one who has to make up less than six missed salah (whether one missed salah or five), he is called ?Sahib-ut-Tarteeb?, he is asked to perform the missed salah first and then in-time salah. Now, you should see in which category you fall and act accordingly. The sahib-ut-tarteeb, in some cases, is not required to maintain order. The detail has been mentioned in books of Fiqh.
Allah (Subhana Wa Ta’ala) knows Best
Darul Uloom Deoband