A button to download individual topic certificates will appear on the topic card in the library after you complete each topic.
Additionally, in the menu on the left hand side of the portal, there is an option titled “Dashboard”. If you click this menu item you will be shown a list of courses that you have completed. From here you can choose to download individual PDF certificates or a PDF Progress Report listing all your completed topics or a "csv" (spreadsheet) of all your completions.