Windows 98 reformatted drive

I have a person who had Windows 98 on a computer and it was running slow. They decided to put a second hard drive in and installed the OS (Windows 98) on it. Then for some reason, on the old hard drive – they deleted Command.com. There is data on that old drive that needs to be copied. Can command.com just be copied from the new drive – to the old drive? Or is there some way to get to this drive? When I try to access it in windows 98, the error “this drive has not been formatted – would you like to format now” pops up.

Any help would be appreciated.

Thanks