I just put my 1st disc brake bike together today. The front pad was rubbing. A Google search lead me to this video. The first part was loosen the screws with the brake depressed. Which I did. Doing it a few times worked. If that didn't work, the second part of the video showed what to do. I purchased a disc brake bike to learn about disc brakes. Similar to a cars disc brakes, I remember pushing back the pistons while working on my old Toyota truck.
I hope this helps.