Sorry to say but we can’t seem to understand what do you mean by having a Custom Side Tab. Can you please elaborate your concern more with image or video so that we can better understand and assist you accordingly.
We are really Sorry for the inconvenience but there isn’t an option available in the Theme for that. It will eventually require Customization and this is out of our Theme Support scope.
You can try out any third-party Plugin in this regard that best meets your requirements at your own risk.