Judy’s advice is very good.
In addition, to help prepare for confession, you might look online for an examination of conscience, for example there are several here: usccb.org/prayer-and-worship/sacraments/penance/examinations-of-conscience.cfm
There are lots of others online as well. You can just poke around and see what helps you most.
Of course, as Judy says, if you forget stuff, your confession is still valid and the forgotten sins are still forgiven. However, a good examination of conscience can help you prepare to avoid committing those sins again in the future.
When I came back to the Church after several years away, I was worried that confession was going to be difficult, but it really wasn’t as bad as I feared. Given that I don’t usually like face-to-face confession (I mean it makes me uncomfortable, NOT that I think there’s anything wrong with it) and that my first confession coming back to the Church was face-to-face, and of course I had years’ worth of sins to confess because even before I left the Church I was sort of behind on Confession, I was scared about going to Confession for the first time. But it really wasn’t bad at all. It was just such a relief to be home again. :extrahappy:
God bless you in your return!