after effects video loop

I need a video tutorial ( no audio required ) which shows how to seamlessly loop a non-looping cloud and waterfall video sample? in adobe after effects. This can be any length but around 15 - 30 second loops would be ideal. This is only for personal use so it doesn't need any captions, I just need to see the method used. Just a video screencap of the process is fine.? The files used in the projects? must be included with the final video tutorial so I can try them myself.