Urgent: Missed Zakat for many years (over 20 years) how to make up for it?

Salam Alaikum, I have been on the wrong path for a long time and Al Hamdulillah recently came back to Islam and been doing my best to follow. One pillar I didn’t follow yet is Zakat, I started doing Sadaqah but I realize recently it’s not the same as Zakat. I just learned that if a person misses Zakat, they need to pay all that they have missed. Which is based on my understanding: 1. Since age of puberty (~12 years old for men) 2. Owning over the amount of Nisab for one lunar year Which means if you have money / assets that are over the Nisab value, then you are required to pay Zakat. Now here is the big challenge: I have no idea how much I owned, and for how long. How do I pay missed Zakat when I have no idea and it’s over 20 years of missed Zakat? Please help me understand and ask me any questions to clarify. Thank you