What should a person who has combined more than one missed obligatory prayer in a day, and does not remember the number of days or missed prayers, do?

Delaying a prayer beyond its prescribed time without a valid excuse is forbidden by Sharia and contrary to Allah's command to establish prayer at its appointed time. It falls under the threat of His saying, the Almighty: "So woe to those who pray, [But] who are heedless of their prayer." (Quran 107:4-5). Whoever delays a prayer without an excuse must repent. In the event of missing a prayer due to an excuse or otherwise, it is obligatory to make it up (qada') and to observe the proper order between the missed prayers themselves and between them and the current prayer, unless there is a fear of missing the time of the current prayer, in which case the current prayer should be performed first. If the number of missed prayers is unknown, one should make up what brings certainty or a strong presumption of being absolved, and it is obligatory to make them up according to one's capacity in a way that does not harm one's body or livelihood.