When investigating an odd field value on a prospect's record in Pardot, the first course of action should be to view the prospect's Audit tab. This tab provides a comprehensive log of all changes made to the prospect's record, including information on what changes were made, who made them, and when they were made. This approach allows users to quickly ascertain the source of the odd field value, whether it was updated through a form submission, manually edited by another user, or changed through some other process. It is a more direct and reliable method than contacting assigned users or reviewing individual form submissions, which may not conclusively reveal the origins of the specific change.