Port Aventura tickets date

Anybody have experience with changing PA ticket dates?

Looking at booking the current 2 day /2 parks promo for price of 1 day (https://www.portaventuraworld.com/en/tickets), but when booking you need to select a date of first visit on a calendar and we would like to await opening hours for our October dates for that, but the promo is only running until end of this month. According to the terms it says "You can change your visit dates as long as the new date of your first visit is in the same season as your ticket." but I'm wondering if anyone knows how?

Is it easy to do yourself online, does it not matter and can you just show up any date as long as it's this season?

Previous years we've bought online as well but then they were just valid all season without needing to select specific dates. I'm guessing this is now because of COVID regulations?

Thank you in advance for any help!