There is an alternative way to open your garage door from your BMW i3 without using Homelink, called Apple Carplay. Your BMW i3 is certified by Apple to use Carplay.
CarPlay is a piece of software that allows your Apple iPhone to interface with your BMW i3's built-in entertainment and information system. CarPlay increases convenience and reduces distraction by putting commonly used apps, that would be necessary or especially useful while driving on your car's infotainment display. By doing so, CarPlay minimizes the need to actually handle your iPhone while driving.