How to update iPhone 6s to iOS 14 to download YouTube?

Hello,

The YouTube app requires iOS 14. Try updating your device, for which you provide no details. When updating, your device will update -if it can- to the highest version currently available that it will support. Here are two different ways to ensure the highest iOS that your device will support is installed on your device.

For instructions about updating your iPhone, iPad, or iPod touch wirelessly, click here --> Update your iPhone or iPad - Apple Support

Here are instructions about how to update your iPhone, iPad, or iPod touch with the Finder on a Mac computer --> Update your iPhone, iPad, or iPod touch with the Finder - Apple Support

If you cannot update, see if you can watch YouTube using a web browser.