When FarApp posts an order to NetSuite, the user listed under the System Notes tab on the sales order will be the one who generated the the access tokens for the role 'FarApp Web Services'. The user is listed in the 'Set By' column and 'Web Services' will be in the Context column in the Create Record line.
To change this user, you can generate new tokens under a different user and add them into FarApp. To do so, follow these instructions outlined in this article - https://support.farapp.com/hc/en-us/articles/115013718667-NetSuite-Token-Based-Authentication
You can skip down to the section that says 'Creating Your NetSuite Token Authentication Credentials'. Where it instructs you to assign the 'FarApp Web Services' role to an existing user, choose a different user.
Once you generate the new tokens, you need to update them in FarApp (the article explains this at the end). Any future orders should then have the updated user listed under the Set By column on a sales order when it's created in NetSuite.