Hi Areti,
Better late than never, but I don't have good news for you.  I'm assuming you mean that you deleted a Recovery Solution account, and the Deletion or Server Space Management job has already run?  In that case it is unfortunately not possible to "undelete" the data unique to that account.  The only thing you could have possibly done would be to restore the database and BLOB files from backup.

In the future, if you accidentally mark an account for deletion, you can still undo it, regardless of what the warning message says (at least up to the point that your next SSM/Deletion job runs).  Just run the following against your RS database (AeXRSDatabase by default):

UPDATE SBS
SET DeleteFlag = 0
WHERE DeleteFlag = 1