First, go to the web and search 'book mock-up.' Images similar to these should pop up. You can directly take these if you wish to.

After selecting your mock-up base, go to Picsart and choose your finished cover, size it as close to the template as you can but don't place it over the binding.

Hit apply. Add your cover again, and size it to cover the binding, but turn down the opacity.

Erase any parts that overlap your first cover. Turn the opacity to your liking.