Help needed on correct procedure for failed disk replacement on SAS 5/iR

I have a PE1900 which was running RAID 1 Mirror with two drives on SAS 5/iR controller. The second disk of the mirror set failed completely and I have replaced it but do not want to take any chances of messing up the existing data on the 1st disk which is fine.

There seems to be no way of simply adding the new drive to replace the old one through open manage server admin as although the disk shows there are no actions available.

I'm guessing that the only way of fixing it is to go into the RAID Bios on boot up but I do not want to make a mistake and rebuild the array in a way that may remove the original data. (We do have a current back up but to be honest I do not want to have to spend hours rebuilding the server if it all goes horribly wrong).

Can anyone help buy pointing me to any documentation that gives clear instructions for the procedure, or better yet, a version of the SAS storage manager that will actually allow me to manage the while thing without re-booting?

I have had RAID disks fail on other Dell servers and never had this problem before as the usually simply recognize the replacement drive and rebuild automatically or have a command in the Open Manage app.

OS is SBS 2003.

Many thanks

John Wilson