Use YouTube Premium to download videos for offline viewing in the YouTube app
Open the YouTube app on your device
Sign in to your account
Find the video you want to download
Tap the Download button below the video
Choose the video quality if prompted
Wait for the download to complete
Open the Library or Downloads section to watch offline
Note that downloaded videos may only be available inside the YouTube app
Check that the video is available for offline download in your region
Make sure you have enough storage space on your device