Recently we've had the case that a developer is no longer working on the project or due to confirming a lot of issues, it was automatically assigned to him.

We wanted to 'unassign' those issues in bulk, but found no such action from the 'view issues' screen.

Issues in 'Assigned' status should revert back to 'New' in case it's unassigned.

Note: There already is an option to 'Assign' them in bulk. This feature might well just add the option to leave the 'Assigned To' field blank, which would then mean we're unassigning.