The feature is live in a few players games as Jam City do further testing. But don’t worry if you’re not one of the players that has it in their game as all players will see the function very soon.
If you’re part of the testing you’ll see the Icon below. Tap it to see the feature. I’m just seeing it myself and I’ll be doing a post as soon as I can.
However be aware players who don’t have the feature are getting a pop up to buy Uranium, please hold off as you can’t use it at this time.