A workstation uses a two-drive RAID 1 mirror for its data volume. One drive failed and was reported by the RAID controller. A technician powered down the machine, removed the failed drive, and installed an identical new blank drive. After booting, the array status shows 'Degraded' and the new drive appears as 'Foreign' or 'Not a member.' What must the technician do so the array returns to a healthy, fully redundant state?