It is not possible to change the field type of a field placed on the form.
For example, it is not possible to change a "Drop-down" field to a "Check box" field afterward.

If you want to use a field of a different type, place a new field on the form setting screen.
Using a CSV file, you can migrate data into the newly placed field.
For details on importing/exporting data, refer to the following pages.

• For steps to export data of an existing field, refer to Exporting Data to a File.
• For steps to import data into a new field, refer to Adding/Updating Records in Bulk.