Welcome home! The best way to prepare for confession is to make a good examination of conscience (see link Guide to Confession). Sometimes it’s helpful to jot down on paper all the mortal sins you can remember since your last confession. After so many years it’s often difficult (or impossible) to remember all your mortal sins, but don’t worry, the priest will help you.
Can. 988 §1: “A member of the Christian faithful is obliged to confess in kind and number all grave sins committed after baptism and not yet remitted directly through the keys of the Church nor acknowledged in individual confession, of which the person has knowledge after diligent examination of conscience.”
The obligation of the faithful to confess in kind and number all grave sins is not to encourage scrupulosity, but to help the priest make his judgment with sufficient knowledge.
And, remember, there is no sin you can commit that God is not willing and able to forgive—all that is needed is true repentance and sorrow for sin. Call your parish office right now for times of scheduled confession, or make an appointment to speak with a priest. In the meantime, please know that I will remember you in my prayers. God bless you!
Guide to Confession