Sometimes it’s easier to just delete the form and create another one using the wizard.
You can add fields using the tools on the Form Controls and Form Design toolbars. If your control is a Data Sheet (grid control) then right-click on the row of field names in the table and choose Insert column. Then right-click on the new column and set the column data field to the desired field. Change the column heading by setting the column label property.
If you have chosen a columnar display (individual text boxes) instead of a Data Sheet control, then you can add a field using the Add Field icon on the Form Design toolbar. You then need to position the field and optionally set activation order. You can also add a text box from the form controls toolbar and hook the text box to your desired data column.