Once you begin a session as a second level character, you still have multiple options for changing your character’s choices. You cannot use Rebuilding (for level 1 characters) or Retraining to build a character that could not be built without using either of those two tools.
Mnemonic Editor: The mnemonic editor hybrid item (Starfinder Core Rulebook page 226 ) allows characters to reverse the last 2 levels worth of decisions on a character. Different versions of the device allow you to retrain up to three additional times, effectively allowing a character to clear and retrain up to 8 levels worth of decisions throughout their career. For more information on purchasing a mnemonic editor, see the corresponding Boon.
Training Montage: The Training Montage and Extended Training Montage boons allow characters to clear and retrain character decisions from all levels. Training Montage is for characters with 12 or fewer XP; Extended Training Montage is for characters with 13 or more XP. For more information on purchasing a Training Montage, see the boon text .