While creating the automation for sending a document, a few options for selecting the first party and/or the second party will come up. These are the signatories to your document. By default, the first signatory will be called the first party; the second signatory will be called the second party, and so on.
If you want to change these names, head on to the document editing page,. At the top of the right sidebar, you should see the first Party. You can click the edit icon next to it to change the name to something more appropriate. You can also add more signatories by clicking on the Plus icon.