On side navigation bar, access the Control Center.

Choose the "Archived" option from Service Desk section

By clicking on it a new window comes where you can find the archived Announcement listed with checkbox on ticket tab.

Once you have selected the Announcement(s), an action bar will appear at bottom of table. Click on the "Restore" button.

A restore confirmation screen will appear. Click on "Restore" to proceed with restoring the selected Announcement(s).