Given the details in your post (no make, model or other clues) I think it's time to call the one that set this up and ask.
Only the RAID 5 and up may support disk replacement. And even then I must know which controller or software is used. Some of them have you use some software or control panel to mark the failing drive for removal then you use that again to add the new drive.
No guessing allowed from my experience.
-> Let me share what usually happens. If the owners can't find out more they usually end up replacing the server or rebuilding it from scratch.
-> Can you reveal how you got into this big hole?
Bob