You can create a workspace in two ways:

​From Dashboard:

1: Click on the "Profile Picture" icon and click on the "Create Workspace" option located at the bottom of the pop-up.

From the Account Setting section:

1: Click on the "Profile Picture" icon on the dashboard and then choose "Account Setting" section

2: Click on the "Settings" tab and under "Team Management" click on the "Create" button

Note: The premium plan that you have purchased is for one workspace. When you create a new workspace, it will be in the Free plan by default.