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.
Data can be migrated by exporting data from an existing field to a file and importing it into a 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.