Generally speaking, you can go to http://9292.nl/ for any itinerary with public transports in the Netherlands. One useful trick is to enter the postal code (3198 LG according to the P&O website) as point of departure or destination. In the Netherlands, a postal code corresponds to a specific street (and not a town or part of a town), so you can use it to find a route without having to worry about spelling the street name right or mixing up different streets of the same name.
In this particular case however, I couldn’t find any good alternative. I don’t have any personal experience with this particular route so I don’t feel confident in recommending it but the only solution seems to be to go to the Pistoolhaven where you can get a ferry to Hoek van Holland (this is called the “fast ferry” and is part of the Rotterdam transit system). There, you should be able to connect to the train and the rest of the country’s public transport network. In this direction, it should take about 2 hours and cost a little over 17 € in total to reach Rotterdam Centraal (3.3€/person for the ferry and 5.3€/person for the train).
However, the way from the P&O terminal to Pistoolhaven looks quite long on the map. If you can find one, it could still make sense to catch a taxi (perhaps sharing it with some fellow travelers) just to go to the Pistoolhaven ferry terminal as it would presumably cost much less than going all the way to Rotterdam and basically divide your travel time in half. From there, the ferry + train connection looks quite good.
PS: I misread the question and described the way from the P&O terminal to Rotterdam but the same logic also applies in the other direction. Unfortunately, the ferry connections are even worse and I doubt you can rely on finding a taxi at Pistoolhaven. One might perhaps be arranged in advance with a local company. A quick google search located this one, you could call them to see what’s possible and if the price is acceptable to you.
Also, walking might not be totally out of the question but seems very difficult, especially if you are carrying some luggage. The ferry terminal is in the middle of an industrial/port area and you would need to take a bridge to cross some river arm, total distance is 8 km. According to the 9292 website this works out to a total of 3 hours from Rotterdam Centraal (train + two different ferries + 1 hour waiting time between the ferries + more than 1 hour walk at the end). The connection between the train and the first ferry is extremely tight so be careful if you are considering taking the last ferry of the day.
Credit:stackoverflow.com‘