No app needed. Sketch a bookshelf. Empty it out if the books are too hard to draw.
Sketch it while standing from the other side of the room.
While sitting on the other side of the room.
While standing/sitting in the middle of the room.
While standing/sitting right next to it.
Pay attention to which shelves you can see the top, and which ones you can see the bottom.
Pay attention to the foreshortening.
This will help you see WHY 2- and 3-point perspectives are a thing, just like how a railroad helps you see why 1-point perspective is a thing.
I randomly drew my bookshelf on a whim one day, and I think I gained like 10 levels in perspective from that one sketch.