“Happiness is an inside job”
― William Arthur Ward
So how do we tap into that inside part of us, if we don't feel happy? Some people can do it on their own, and others may need assistance. The formula is simply to find a place in your memory that you can connect with, that gives you those happiness feelings. It doesn't matter how far back you need to go to find a memory.
See that event in your mind's eye, relive that event and feel into the same feelings as the first time this took place. Stay in those feelings for as long as you can. Remember what was going on around you, and who were you with? What were you wearing? What time of year was it? Recall all the details you can. The more you can tap into the feelings and recreate them now, the more you will bring the happiness forward to today.