There is a code sample in the readme. This is not super straight forward due to the way SF doesn’t have default fields do any of these, so you have to map them to custom hidden fields.
Thank you. And I assume that’s done in the Form Editor tab?
I saw that the source field id in our salesforce is lead_source. MY question is: Which label or value do I need to put in the field mapping table, in order for the plugin to pass the utm to the “lead_source” field?
Hidden fields are added in the Form Editor, then you use the sample code to autofill them with the data from the query string (utm info).