OpenGameArt.org
Calm Relax 1 (Synthwave 421k)
Credit line
"Calm Relax 1 (Synthwave 421k)" by cynicmusic licensed CC0: https://opengameart.org/content/calm-relax-1-synthwave-421k Author's attribution notice: ATTRIBUTION: The Cynic Project / cynicmusic.com / pixelsphere.org
Where to put it: Game credits or video description. If the entry has a "Copyright/Attribution Notice", follow that.