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.
Cleanup API is available at: http://confluence_server/confluence/confiforms/cleanup.action?pageId=PAGE_ID
PAGE_ID is the id of the page where ConfiForms form is configured
You can use it to cleanup data stored by ConfiForms plugin, all data or filtered by filter criteria
Same format as for filters is used: ConfiForms Filters
If your confluence server runs in a root context then the URL will not include /confluence