Courses are only allowed to count once toward a credential requirement. When you have completed a course from a credential topic, it will no longer be accessible from the 'training that applies' section of the credential details page.
Activities can count multiple times towards a credential topic and there is no limit, however, you will notice when you complete an activity, it is no longer accessible from the 'training that applies' section. In order to allow the user to complete the activity more than once directly from the credential detail page, you would need to adjust the activity settings to allow self assign. Please see our help article titled, Allowing Self-Assign, for further assistance.
There is not currently a way to have TargetSolutions or SCORM courses count more than once, regardless of the method in which the user accessed the course.