You are going to find Therapy in the right hand column under Bank and above Help / FAQ. What the Rockstars Live Therapy does is allow you to pay to replace your Confidence. In Rockstars Live Confidence means the same thing as health. It has been mainly changed because people rarely die from a savage series of guitar battles. If you are at full Confidence already, you will be told that when you enter the Rockstars Live Therapy and you will not be able to use the function.
Once you are not at full Confidence, likely through Battles, you will find that there is a green Restore button in the middle of your Rockstars Live Therapy display. There will also be a price in the button, and that price will be relative to how much Confidence you need restoring as well as your position in Rockstars Live.
You are required to have money in the Rockstars Live Bank to be able to use Therapy. You cannot just pay your Rockstars Live Therapy bill with spare money, it has to be from the Bank. Make sure that you have a balance in the Rockstars Live Bank before you try to use Therapy, and that the Bank balance is more than the cost of the Therapy.