Unfortunately, moving from tables to a command is not quite the same as changing the individual tables.  So, there is no simple way to remap the fields on the report from one to the other.  I suggest that you don't delete the tables immediately after adding the command.  Instead, use the table fields as a key to where the command fields are supposed to go, then edit all of your formulas prior to deleting the tables.  Then, when you run the report for the first time, Crystal will let you know whether you've missed any mappings in formulas and bring them up for you to edit while it's trying to run.