What action is not necessary when using the CAR form for updating attorney information?

The correct answer highlights that paying an additional fee is not necessary when using the CAR (Correspondence Address and Registered Attorney) form to update attorney information. This is significant because the USPTO allows for certain amendments to be made, such as updating attorney details, without incurring extra costs, making the process more accessible for trademark applicants.

In contrast, entering serial numbers is essential as it identifies the specific trademark application requiring attention. Reviewing updated information is crucial to ensure accuracy before submission to avoid any issues with processing. Finally, submitting the form after updating is, of course, a necessary step in completing the process. Without submission, the changes would not take effect. Thus, the process is designed to facilitate updates without adding a financial burden, which upholds a user-friendly environment for trademark applicants.