How do I find a lost pair of Beats headphones?

Which exact model is your Beats headphones? What device(s) are you going to use Find My with to try to locate them?

Ref: https://support.apple.com/guide/beats/locate-your-beats-using-your-apple-device-devfa3444893/web

Ok, thanks for the update. Have you reviewed the support article I provided you? ... and, if so, what were your results?

Your Beats Studio Pro headphones can participate in the Apple Find My network, but they needed to be paired with your Apple Account before you can use the Find My app on your iPhone to locate them ... and, if you already did that, if they are not appearing in the app, then either one or more of the following could be the reason(s) why:

• There were no other iPhones within Bluetooth range of it. Shouldn't be an issue if you are in New York city.
• The Beats' battery is depleted.
• The Beats are such located that they cannot be able to be "seen" by nearby iPhones.