From the introduction:
This module is designed to take 2nd level characters up to 3rd level. For most classes, this means picking an archetype, tradition, or oath. Some classes, such as Cleric, pick this at level two and it is okay if the players have already selected their class specialization. At the end of this module, each character will be given the chance to apprentice with a master of their class. As apprentices, they can pick their archetype, tradition, or oath, and it is recommended that players who have already selected this for their character (e.g. Clerics and Druids) be allowed to change it at this point if they so desire.