Breathizen is sold with a 60-day money-back guarantee, running from your purchase date. Diary the day-60 deadline the moment your order arrives, since that is the part people forget.
Contact customer support directly — not this website — within the 60-day window, describe your experience, and ask for the refund. Retain your order confirmation until the process is completed.
Note that the 3- and 6-bottle packages carry enough servings to run well past the 60-day guarantee window — make your decision on the earlier part of your supply, not the last bottle.