If you're wondering how to get the IDs of the user you'd like to report:
User Settings => Appearance - Scroll down to advanced, click the toggle switch on Developer Mode
Once enabled, just right click the user and click copy ID. :)
MOBILE
(Android) User Settings => Behaviour - Toggle the Developer Mode Switch.
To get the ID (Android) : Get to the users profile, scroll down to Copy ID.
(iOS) User Settings => Appearance - Advanced and toggle the Developer Mode Switch.
To get the ID (iOS) : Get to the users profile => Tap on the 3 dots => Tap Copy ID.