Hi Maulik!
Sorry to hear the audio button is absent when revisiting slides in your Storyline course!
Thanks for sharing your file! After publishing the course to Review 360, and testing the behavior on my end, I was unable to reproduce the same issue.
Upon revisiting previous slides, the audio button was present and functional. To clarify, are you observing this issue within Storyline, Review 360, or through your LMS? If the issue can only be observed on your LMS, testing your file with SCORM Cloud is a great first step. This will help determine if the problem lies with the .story file, or the LMS itself.
Looking forward to hearing from you!