Click on it, and you can now use any kingly title as your primary, including a titular one like King of Galicia. Click on the secondary one and then a button labelled 'make primary' will appear next to where 'create title' would be. Once you have more than one royal title, you will be able to click on the secondary one at the bottom of the screen, where all your titles' COAs are arranged in a row. Click on your COA in the character screen and IIRC you will end up on the screen where you can see your treasury expenses and income, as well as create new titles.