This is the documentation for ConfiForms Server/Data Center app
However, this might also work for ConfiForms cloud and in most cases it does. But please see this page to understand the differences between server and cloud versions of the ConfiForms app.
Import API is available at: http://CONFLUENCE_SERVER/confluence/confiforms/import.action?pageId=PAGE_ID
PAGE_ID is the id of the page where ConfiForms form is configured
And supports CSV formats for data importing.
To start with data importing you need a ready ConfiForms form as the importing API expects you to set the mapping between columns and ConfiForms fields.