how to change device number in RAID array

[Gary Dale]

I'm running Debian/Bookworm on an AMD64 system. I recently added a 
second drive to it for use in a RAID1 array. However I'm now getting 
regular messages about "SparesMissing event on...".

cat /proc/mdstat shows the problem: active raid1 sda1[0] sdb1[2] - the 
newly added drive is showing up as [2] instead of [1]. Apparently mdadm 
thinks there should be another drive sitting around as a spare.

Is there a simple way to fix this?

Thanks.