Verified answer

You can't erase a CD-R type disk - it is permanent..

To un-erase it would be to erase then replace erased content so therefore not possible.

If using a CD-RW (re-writable) disk the contents can be erased but the disk will have to be re-burned to replace the erased contents - it can't be un-erased.

You don't say what type of disk you are referring too so this answer is guesswork.