The LearnDash Resume Button module enables a shortcode, [uo_learndash_resume], that allows signed-in users to immediately return to the last LearnDash post (course, lesson, topic or quiz) that they visited. Adding the shortcode will create a button (which will adopt any styles set for form submit buttons on your site) that’s visible to users that have visited at least one LearnDash page.
Since this is a LearnDash page (a lesson), the resume button cannot be placed here because it would link to itself as the most recent LearnDash page visited. So a working demonstration of this button (accessible to logged-in users only) is located on the Course Dashboard page.
Visit the knowledge base for full details on the LearnDash Resume Button.