This seems like one of those digital marketers preying on the mentally ill. I doubt there's any groundbreaking information in that book. Some mixture of diet and exercise + reflection on life and slowly solving your endless list of things you aren't happy about.
I would suggest looking into foods that are rich in tryptophan, tyrosine , phenylalanine (amino acids that are precursors to serotonin, dopamine and norepinephrine). Another thing is probiotics - kombucha, sauerkraut, kimchi. Some people make their own and it's a fulfilling hobby.
Look for some kind of fun physical activity that you enjoy. May be dancing, martial arts, walking, trying to do a cartwheel.
Write down something you don't like in your life. Can you change it? If no or not yet, move on to the next thing. Little by little, you can accomplish a lot.
Trust me, the work is worth it. Being out of depression is crazy.
As a bonus, I would suggest looking into some buddhism type teachings a la Alan Watts or something of the sort. Let go and vibe ~~~ Don't be attached to an outcome.