While creating the automation for sending a document, a few options will come up for selecting the First Party and/or the Second Party. These are the signatories of your document. By default, the first signatory will be called the First Party, the second signatory is called the Second Party and so on.
If you want to change these names, head on to the document editing page and 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.