To obtain your 3rd Class, you must first reach Level 10 on your main class. Once you’ve done that, head to the Class Hall in Varanas and choose a secondary class. After selecting your secondary class, you will receive two teleport spells in your Skillbook (Default: "K")—one to Reifort Camp (to help level your secondary class) and another to Heffner Camp, which you’ll use later for your third class.
Exclusive Classes:
To unlock the third class, you need to level both your main and secondary classes to Level 20. Once you reach
this requirement, a popup notification will guide you on what to do next. At this point, you need to visit Johnny Dutin in Varanas (Eye of Wisdom) and complete his quest, "The Price for Improvement: A Promise" (424346) Simply talking to him again after accepting the quest will complete it.
After finishing the quest, you’ll be able to select your third class. You can then use the Heffner Camp teleport
spell in your Skillbook to travel to the Coast of Opportunity, where you can start leveling your new class.