If you happened to have set, accidentally set Parental Control Settings for less than 17+, then you won't be able to download youtube. Now go back up to the instructions for iTunes and you should at this point be able to get it back. If the App says that it is downloaded, then click on Purchased on the right, click on Not in My Library and find it there, and then download it. If you don't see the app on iTunes, you may have to go to the iTunes App Store to download it. There will be a list of Apps, scroll down to find YouTube.Click the device icon on the top left side of iTunes.

If that isn't working and you have updated your apps using iTunes

Press Not on This iPhone or Not on This iPad.

Press Purchased at the top of the screen (only for iPhone).

Press Updates for iPhone or Purchased for iPad in bottom menu bar.

You should see the app downloading right onto your home screen. After you do either of these options, go into the App Store and try downloading it again. To turn it back on again, press and hold the button again, or plug the phone in if your lock button isn't working. Slide the slider that appears to turn it off. To turn your phone off, hold the button on the top of your phone (or the one on the right-hand side if you have an iPhone 6 or 6 Plus) until a slider comes down.

Turning your phone off and back on again.

On iOS 6 and earlier, where Control Center is not available (nothing happens if you swipe up from the bottom of the screen), do this from Settings. Doing this will turn the cellular radio and the Wi-Fi connector off and back on again.

To do this, swipe up from the bottom of your screen and tap the icon for an airplane. Switching your phone on Airplane mode and back off.If the iCloud icon is greyed out and nothing's working, try.

Use the App Store app to download YouTube onto your phone.

Download youtube app