To assign or un-assign dashboards to multiple users, head over to Account Management from the hamburger menu on the top-left corner of the navigation bar.
Select the users to whom you'd like to assign or un-assign workspaces, and click the Dashboards button from the table toolbar.
On the modal window that opens, use the radio button to choose Assign or Un-assign, and the checkboxes to select the workspaces listed under their respective dashboards.
To confirm your selection, hit the Assign (or Un-assign) button from the modal footer.
Note: Only Account Administrators have privileges to assign or un-assign dashboards and workspaces.