Why, do I have to now? It's been superceded by the 1983 Code of Canon law, has it not? And I did not find about this secret rule until 2003.
You have started your countdown of 90 or however many days since you now know :-).
All you are required to do is seek out a different confessor, tell him what happened and he decides if you should take it any further. If you want me to look it up for you I can do that tomorrow if I can find the book.