To download your certificate, you can go to the Student Profile page, find the course or assessment title, and click on the paper icon to the right of the title.
You can also go back to the assessment page, where you should see a “You’ve earned a certificate!” message at the top of the page with a “Download Certificate” button that should allow you to download the certificate easily.
Certificates can also be downloaded by scrolling down your list of courses on the Student Profile page and finding an Earned Certificates section at the bottom. The link(s) here will also allow you to download your certificates.