There MUST be a REBUILD option. There is no point of having a RAID5 array otherwise.
It may be in your BIOS (DEL key?).
I'm not an expert on RAID. I assume REBUILD means it will just rebuild the new drive to MIRROR the others.
You should have a manual, or can download one.
My BIOS has a REBUILD command when I enter it and then enter the link to my RAID.
I think I've got my answer.
No, there's nothing in the BIOS that does this.
When pressing Ctrl+F, AMD's ROM Utility comes up. You can't do it there either.
I think you have to use RAIDXpert. FYI, the default username and password is "admin" and "admin".
I'm running some tests now to see if this is my solution.