Enlarging part of an image on photoshop app

I'm working on a sticker design, I sketched it by hand and uploaded to my photoshop app. Once I am nearly finished I noticed that the posportions are off.in other apps I'm able to that part and enlarge it. How do I do that here without creating it all over (which I don't have enough time to do ) if try to select it using the margins whatever its called I can get it exactly the right proportion but once I try and move it it created a blank place and doesn't more the image selected just the area and the lines are all messed up. Help!