When you open process design page and then click on Databases, you will see a list of all relational database schemas tied to that process. If there is no schema yet you can simply click Import and add one of the existing schemas or Add New Schema to create a schema and its tables. All of the schema import, update and add operations are not executed until the process graph is committed.
Import
Displays all existing schemas. Select the ones you want to include in your process and click Ok.
...