If you want to use the ideas of Zen to help yourself feel better, there are any number of ideas that you can use.
You can treat everybody you encounter with kindness.
Another idea is that all of your problems stem from your thinking. If you believe that, you should be motivated to change your thinking.
A powerful idea is that enlightenment is possible. There is great comfort to be had in that concept. That means that there is a way out of your suffering.
One idea is that everything is constantly changing. When you apply the idea of impermanence to your mood, you know you will not be stuck in your current mood for too long, because it too changes.
There is the idea that you are perfect as you are, just like Buddha. If you believe that, you will not struggle with self esteem.
Speaking of self, there is the idea of no separate self. That idea connects you to the entire universe. It is as if your pinky toe had the idea that it is somehow connected to all of the toes on your foot and even to the toes on your other foot. If you understand that idea, then the other Zen ideas will become clear to you.
Any of these ideas can help you feel better if you find them to be true. If you don’t want a preconceived idea, just sit and meditate. See what occurs to you. There are millions of Zen ideas to help you feel better, or you can just listen to the raindrops. That is nice too.