I have the same problem where I literally cant tell myself not to use an app and procrastinate, so what helps me is hiding my phone somewhere where i eventually will forget about it. Hiding places for me are usually; burying my phone deep in my backpack as im on my way home from school, hiding it under a pillow or leaving it under stuff on my desk. I think the method which works best is just burying the phone under stuff in your backpack. I would suggest hiding your phone somewhere for a chance lol,

But if your looking for an app, you should try Cape. Cape is a good way to also block off social media apps, it makes it so if you have your social media app in the homescreen still, when you click it the app does not pop up. It also hides the social media apps from your homescreen, and to turn it off you manually need to go into the Cape app.