I created a form and mapped the form to a table - everything is working fine and I have collected a lot of contact data in my table.

I then need to add a hidden field to the form and I want the calculated results of the field to be stored in the table.

I went to the Data Manager and clicked on edit Edit Mappings.  I can see the new hidden field on the right side under form fields with an open radio button, but I do not see any way to add this field to the mapping.

I then chose Delete Mappings under Data Manager.  Redid my mapping from the form - had to save the data under a new table name - and then was given the option of importing the data from the XML file.  I did this and it gave me an error message that that new hidden field did not exist - I clicked on continue and my data did not come in.  I then went back and clicked delete next to the error message and to no surprise the data did not come into the new table.

How should I be doing this?

Got it figured out. I deleted the mapping. created the new table from the form. I unmapped the new field and imported the data. Then I mapped the new field.

In the first step did you create the new field in the database before you tried to map the new field? You should be able to edit the mappings without deleting all the mappings.

How do you create the new field in the database? 

You need to be faimiliar with SQL Data Definition Language to add and remove fields in tables, Or have access to SQL Server Management Studio and be able to connect to your Database.