how to install iTunes on new iPod touch 7th generation

There is no app named "iTunes" on iPhones, iPads, or the iPod Touch. There is a "Music" app and an "iTunes Store" app.

If you can't find those apps using Search, you can reinstall them. See instructions in Delete built-in Apple apps on your iOS 12, iOS 13, or iPadOS device or Apple Watch - Apple Support

Ah, you mean iTunes on a computer, not on the iPod.

If you're using a Mac with OS Catalina on it, you add music to the iPod using Finder. iTunes is not used on a Mac using OS Catalina.

See instructions in Use the Finder to sync your iPhone, iPad, or iPod with your computer - Apple Support

iTunes should already be installed on your Mac.