You can import into a List field using values that are predetermined when the field was setup. This makes it so that users can only import specific values into the field to prevent incorrect data input.
Single Select
To import into a single select type list field, the column header must match the field name and the list option values must match on your spreadsheet.
To Import into this field, setup your spreadsheet as shown below. If you are updating existing forms, ensure the form number is filled in. Note: Leaving the Number field will create a brand new form.
Multi Select
Similar to single select options, the column header must match the field name and the list option values must match.
If you want to select multiple options, your options must be separated by a comma. Set up your spreadsheet as shown below.
Further Reading: