Take a look at this thread: https://answers.unrealengine/questions/182054/stuck-on-verifying-process.html 
" just encountered the same issue. Noticed that I was somehow logged out of the Epic Games Launcher. Logged back in and verification continued and install completed.
If you’re logged in and encountering the issue, try logging out and back in. I’m currently on an unstable internet connection which I suspect is the reason I happened to log off; you should confirm that yours is okay. "
Or just wait a little bit longer, because this step takes a while.