Seldom video can spread virus on Android (Linux). Did you notice which app sending you the notification? Maybe the app is too fishy. At least, I don’t think the system will send you such notifications.
Personally, I never install any antivirus on my phones. Linux (Android is using Linux Kernel) machine do not need any anti-vius up to now.
If you really think you phone got virus (possible?), you can try the free antivirus (e.g., https://play.google.com/store/apps/details?id=com.avast.android.mobilesecurity) from Google Play store. I never use such products, so I don’t know which one is better.
If you want to clean your phone, you can do a factory reset (backup your data, but disable Automatic restore in Settings–Backup and reset)