Hello!
Many users asked us to support the option for converting custom fields, so, we added the option to convert text fields into list field and convert list fields into text fields!
In order to convert a field, go to Settings - Fields - Press on the pencil icon next to the field you want to convert.
Next to the field format selection, you can see the options: ‘convert to List’ (for text fields), or ‘convert to Text’ (for list fields).