First, make sure that your website template is connected to a plan – you should see a banner under the template thumbnail.
Access the store settings from the dashboard
On the My websites page, hover the mouse over the three dots on the template thumbnail and click on the Store manager.
Or, go to Settings → Online store → Open store manager.
Access the store settings from the editor
Within the editor, find the store page/section, click on the store block and then click on the Manage store.
Or, click on the Online store button on the left toolbar → Open store manager.
Or, you access the store manager via website settings from the left toolbar.