If there are flags defined on the Bugzilla server Deskzilla will download their settings with the rest of the configuration when a new connection is added and will display controls for working with flags. However, if you added flags on the server after the connection was added, you need to reload the configuration (press CTRL + F5 or select Connection | Reload Bugzilla Configuration).
To add a flag open the Edit Flags dialog by either selecting the bug in the Bugs Table and clicking the Edit Flags button 
on the Bug Toolbar or right-clicking the bug and selecting Edit Flags.
