The proper way of performing Qada-e-Umri is to start praying a Qada prayer with every Fard (compulsory) prayer, for example, Fajr with Fajr, Zuhur with Zuhur, and Asr with Asr. The way of praying an individual Qada prayer to make a Niyyah (intention) before praying it that, for example, I am praying the first Fajr Qada Salah that is due towards me, and the same with all other prayers. And then keep doing it every day.
The person should also write a will that he is starting to pray Qada-e-Umri from that date, and will be praying one Qada(missed) Salah with every Fard (compulsory) Salah, and that he has three years of Qada Salah due towards him. However, if he dies before praying all the Qada Salah, then the Fidyah (compensation money) should be paid to needy people from his estate.
If a person does not leave such a will, then it is not Wajib (necessary) for his inheritors to pay that Fidyah. In Shariah, a person has full disposing authority over his assets only in his life, and before any terminal illness starts. If someone develops a terminal illness then they can dispose of only up to a third of their assets. It is not permissible for them to dispose of more than a third of their assets. So, if a person does not make a will for paying Fidyah while still alive and not suffering from a terminal illness, against his remaining Qada Salah upon his death, then it is not Wajib (necessary) for his inheritors to pay the Fidyah for his Qada Salah even if he has left behind hundreds of thousands of rupees. However, if they wish to do so out of their own free will, then they have the right to do so.
That is why everyone should make a will as soon as possible that if he dies before he is able to pray all the Qada Salahdue towards him, then the Fidyah (compensation) for the remaining Qada Salah should be paid from his inheritance. And he should also start praying the Qada Salah one by one from today. If a person starts doing these two things, then if he dies before he can pray all his Qada Salah, Insha’Allah he will be forgiven. But if a person doesn’t do these two things, neither he starts praying the Qada Salah, nor does he make a will for his remaining Qada Salah in case of his death, then he is being neglectful of one of the greatest Ibadah.