how do I rename a device on my apple ID?

It depends on what device you want to rename.

To change the name of an iPhone, iPad or iPod touch, go to Settings > General > About > Name.

To change the name of an Apple Watch, go to the Apple Watch app on your iPhone > About > Name.

To change the name of a Mac, go to System Preferences > Sharing.

See the Apple Support article(s) below.

Device Name Change.