https://www.epo.org/en/node/epo-designated-or-elected-office-2

Where can I find out more about the procedure before the EPO as designated or elected Office?

Details of the steps to take to enter the European phase, including those relating to representation, and of the subsequent procedure before the EPO as designated or elected Office can be found in Chapter 5 of the Guide for applicants: PCT procedure before the EPO (Euro-PCT Guide).