Folks on here are users just like you, with jobs, and lives - there's no one here who is paid by D-Link to hang around and answer questions as soon as you ask them, so, when using a forum, patience is a necessity - the information you seek is available in the manual, in this forum and in D-Links FAQ, and had those instructions been followed, you would not be in the situation you're in
Essentially you identify the failed drive - either from the LEDs, the status page or the email you told the DNS-323 to send you - you power down, remove the failed drive and replace with a new one, power the system back up and log in, at which point the system will prompt you to format the new drive, and then reboot, after which it resyncs.
As a result of your tinkering, you now need to backup your data, reformat the array, and restore the data.
Good luck.