[Q] Call on hold topic

When I am on the phone and a second call comes in all I do is answer the call and the first call is placed on hold automatically. Problem is when I try to return to the call on hold, I can't. I tap the Hold banner, I tried swiping, I've hit the menu button looking for some way to return to my original call, but nothing. And when i press "end" it cancels both calls. I hear about these "place on hold buttons" but I've never seen one. Any one with help it will be greatly appreciated.
Thanks,
Michael S