The "Reset bookmarks" option must be enabled when a new SCORM file is uploaded to the existing SCORM unit. By selecting this option the users that are still in progress on this course are able to see the new content. Users that have completed the course do not get affected by this action. But in order for the users that have not completed the course yet to be able to access the content of the new SCORM file, this option must be enabled before saving the unit.
You may also refer to this related article when updating the SCORM unit - How to update the SCORM unit?