A user with iris-admin privileges can delete these mnemonics.
From the main menu bar select Configuration. Click Views and Edit Mnemonics from the dropdowns.
You can subset the list by searching for the device in the selection boxes.
Then you can delete the mnemonics by using the delete icon in the Actions column. You can also bulk delete mnemonics by selecting more than one mnemonic fro the Sel column and then clicking the delete icon at the top right of the screen.
To undelete mnemonics, click on the eye on the top right of your screen. This will show all the mnemonics that have been deleted or archived (in italics). To undelete these, click the icon in the Actions column next to the relevant mnemonic/s.