What you need:

Superimpose

What you need: 

A cover 

And a mockup of your choice(the next chapter is filled with them)

1. Open your mockup in superimpose and then your cover  on the home page there's an icon on the  top of the screen that's a hammer and a wrench click that. Now it will ask if you want to edit the foreground or background click foreground.

2. It will come up with perspective choose the perspective that fits you right mockup angle and then move each corner until it fits the mockup then click the check mark and save your work then your finished.

I hope this tutorial helps! The next chapter will be full of mockups for you to use! And if you'd like a tutorial for my new gif signature let me know and I'll gladly make one!