If you haven't done so, download the Remote app onto your iOS device from: https://itunes.apple.com/us/app/remote/id284417350. If you've already downloaded it, delete the app on your iOS device, re-download it, and follow the next steps.
After you download and install the Remote app onto your iOS device, open it and tap on the "Turn On Home Sharing" button (do not tap on the "Add an iTunes Library" button). Then you will be prompted to insert an Apple ID and Password. Please type your iTunes ID which your Apple TV is signed in to. Once you enter the ID and the password, you will see the "Home Sharing" screen, which will simply inform you that now it's active and that you will be able to control iTunes and Apple TV. Then tap on the blue "Done" button in the top right corner, and then tap on the Apple TV photo/graphic on the next screen. After that it will take few seconds to connect to your Apple TV, which then you will be able to control your Apple TV with your iOS device running the Remote app.
I hope this helps. Good luck!