Keith here, I’m a part of the Support Team at Shopify! :)
The current format you have set up is as a standard text field that only offers Bold or Italic changes. Using the same section you can add a "Page" instead of "Text" section. This will allow you to link content directly from a page.
You will want to copy the current content over to a page in the Online Store > Pages > Add Page section of your admin. Once you have the content saved, you can use the full rich text editor to add a link. Select the page you from the section in the dropdown box in the theme editor as shown here.