Just as it requires public heresy for heretical clergy to lose office, it requires public profession of faith to regain one's communion with the Catholic Church. After that:
5) Do a good examination of conscience and make a GENERAL CONFESSION of all the sins you have committed in your life to a priest in the Heavenly Host (e.g. St. Dominic). Remember that being outside the Church, you did not receive remission for any sins at all, no matter how many SSPX, CMRI, etc. heretics and schismatics you went to for confession - since you were still in the mortal sin of schism (either all sins are forgiven or none).
6) Do penance, yea, resolve to live a life of penance and avoid all sin.
Just because we have no known Catholic clergy does not mean that we cannot be saved. We should pray the Rosary daily, begging for contrition for our sins. We should make good examinations of conscience and progress in the virtues, so that we may not vainly hope to obtain the riches God has promised His faithful.
Due to the immensity of the great apostasy, however, it may be difficult for some to fulfill this discipline, since it is also a Church discipline that we may not commune with heretics and schismatics. But bad willed heretics and schismatics want our approval, they want us to slip up and accept or condone their evil lives or beliefs, and thus drag us to hell also. Considering this, if you do not know of any Catholics or good willed people you can abjure before, then you may abjure before non-Catholics if necessary BUT ONLY DO SO IF YOU ARE CONFIDENT that you will be under no temptation to commune with them in any way - otherwise, do the abjuration and profession of Faith ALOUD, UNDER OATH, on your own, SIGN IT AND DATE IT and keep it on hand, with the intention to get good willed witnesses to make it public as soon as possible (you could record yourself on video or audio if you wanted to).
Remember that abjuration is a discipline, and the Church did not institute disciplines so that we might imperil our salvation, but to help us secure it, by the fulfilling of justice and the removal of scandal.
What Must You Do To Get to Heaven?