Click on the Main menu button at the top right of the screen and choose Pages and collections from the Create menu.
Find your PDP collection, click on the three vertical dots at the bottom right of it to expand the menu and choose Manage from the dropdown list that appears.
This will list the pages in your collection.
Use the up and down arrows next to the relevant page title in the Pages already in collection column to move the page to the correct position in the collection. Alternatively click and drag the page title to its new position in the list. You can also delete a page using the red cross to the right of its title from here. When you have finished click on the Next: Edit access button and then click on the Save button on the next page.