Now there are many apps all around that can be used, and that are used to manipulate pictures, but I have only ever used these two apps.

Picsart

Now Picsart isn't only for Manips, so it's a good app to have around when your an editor on the go. I use it for Maniping mostly.

Magic Eraser

Now this is just an app to use to crop out the section of picture you want to put on the original one. I usually go right back to Picsart IF I use this. It's just a much needed app if Picsarts new cropping annoys you.