@mention teammates so the reason is easy to scan on the Alerts table and details.
On alert details, click the pencil next to Description. Make your changes, then click Save. Use Edit alert if you also need to change the title or status.
Block types
Type/ in the description to insert a block. You can also type the shortcut.

Mention a teammate
Type@ in the description and choose a teammate. Their name is added to the note. Assigned to is separate. That field is who owns the alert.
