In the traditional times there was no RCIA, only the rule that new converts shall be instructed about the Catholic Faith and shall make the Tridentine confession. They received a few informal instruction from the priest.
The RCIA was introduced is 1975, as the way to provide instruction to the newly baptized adults, and later extended to instruct the converts too. Some traditional churches have RCIA some do not.
In your case I would talk to the priest at the Church where you attend Masses (supposed theu are in full communion with Rome), and would listen what he says. Legally you are allowed to enroll into RCIA in any parish with full communion if the Church, or receive the instructions without RCIA