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.
In ConfiForms, since version 2.0 records are not deleted completely to keep the auto-numbering rolling correctly.
But sometimes there is a need to "start over" with fully empty form. Deleting all the record will not reset the sequence for auto-numbers, but there is a way to do that
We have explained this briefly in Release Notes#Version2.0.4
Here is a bit more detailed explanation
So, you will need to create or download a file with the following contents
{"data":"<list></list>"}
And use Migration and Recovery API to get it uploaded to your form, replacing everything in the dataset of this form with an "empty dataset"
This will reset the auto-numbering sequence, as well as remove ALL the data stored within this form