There are a few ways a you can mute issues:
Directly on the main dashboard page by hovering over the title of the entity you'd like to mute, and clicking the bell icon.
A banner at the top of the page will appear explaining what was muted. You can click on this banner to edit the mute details (such as what sensors it applies to and the duration).
Mutes can also be accessed from the settings pages under Alerts
Here you can add/edit/delete all mutes
Note: mutes are company wide (and not user specific)