To join the Dolphin Craft, simply go through Chargen for character approval, with your character aged appropriately for the rank you wish to start off at, and your background reflecting you making it to that rank. As an Apprentice, you mention joining the hall as an apprentice in your +info. Journeyman? Working your way there and having been promoted to the rank. After getting through the first hurdle of approval through Chargen, use the Crafter exit as you push through.