The ferry only runs to Sorrento from Procida on Monday/Wed/Friday (from April 1st to Sept 15). and then only once or twice a day.
You could take a ferry to Naples, a ferry to Capri, and another ferry from there to Positano. Use this page for schedules between Pocida>Naples, Naples>Capri,Capri>Positano, The ferry between Capri>Positano has very limited runs and can't dock if weather doesn't allow. This will also be expensive.
https://www.sorrentoinsider.com/en/ferry-schedule?from=capri&to=positano#
You could also take a ferry to Sorrento from Naples and SITA bus or private driver to Positano.
https://www.sorrentoinsider.com/en/sorrento-to-positano-bus-schedule
https://www.sorrentoinsider.com/en/ferry-schedule?from=napoli&to=sorrento#
Or transfer from the Naples port to Napoli Centrale train station and take the Positano Shuttle (I haven't taken this personally):
https://www.positanoshuttle.com/service/naples-to-positano-or-praiano-shuttle-bus-booking-page/
Or transfer from port to train station, take the Circumvesuviana or Campania Express train to Sorrento and SITA bus or private driver from there.
Or private driver from Naples. This will, of course, probably be the most expensive option. A search for "driver, Naples, Positano" will bring up some past suggestions. Monetti Taxi (now called Sorrento Top Driver) has been recommended often:
https://community.ricksteves.com/travel-forum/italy/private-driver-in-positano-amalfi-coast-area
