Since version 2.11 of the Dashboard, you can search for a badge, a user, or an organisation using the search bar. To do this, go to the corresponding menu ("Badges" for a badge; "Users" for a user...), then enter the name of the item you are looking for. For a badge, you can also enter its MAC address.
❗ Make sure to open the corresponding menu before performing your search. If you're looking for a user but you're in the "Check'In" menu, your search will not return any results.