[SOLVED] help

On the song page, click on the "Edit" button at the top of the page, then put the link to the YouTube video in the "Video URL" field, then click on "Save" at the bottom of the page.
Screenshots: https://imgur.com/a/LGyu1UZ

You can do so directly while first publishing the song (no need to edit later), since there's a "Video" field there too (at the bottom of the page).

One other thing: please divide the lyrics you post into stanzas whenever possible, thank you.