If you are over the age of 18 and have received your First Communion in the Catholic Church and you would like to be Confirmed Catholic you’d participate in an adult Confirmation program. Adult Confirmation programs are held throughout the Archdiocese of Chicago each fall and spring. Please see https://pvm.archchicago.org/lifelong-formation/about-us for class locations and dates.
If you received your First Communion in a Christian denomination that is not Catholic (Lutheran, Baptist, Methodist, etc.) and want to become a Confirmed Catholic then you would participate in RCIA.