Currently, Instagram doesn't allow shares to be made from outside their app, which means you can't click on a link from an outside source and share on Instagram. Therefore, Instagram Share button is not currently available.
Because of that, it is simply not possible to have an Instagram Share button (at the moment). If this changes in the future, we will add the Instagram Share button as well to our product.
You can, however, have a Follow button on our Horizontal or Floating Follow bars, so people will follow your official page on Instagram. That way you can gain more followers organically and grow your Instagram account.