Configuring replacement drive in MyBook Duo

One of the drives in my 8TB MyBook Duo (RAID 1 configuration on Mac OS 10.14) failed. I replaced it with an identical drive and now not sure how to restore the Raid configuration. It’s not quite clear what to do in WD Drive Utilities. Do I just hit the Rebuild button in the RAID Status tab? Under Drive 1 Status (the one that failed) it says to Click the Configuration tab to use the new drive, which gives me options to specify the RAID configuration and I’m supposed to acknowledge that changing the drive configuration will permanently erase all the data on the drive. Does that apply only to the new drive, or both? I assumed, perhaps naively, that the RAID configuration would allow me to propagate the data from the working drive.