How to update the log file or create a custom log file for tomcat-access.log with new fields inorder to have more details like username and the action of user

I suggest to contact Appian to discuss a product enhancement.

hi [mention:7b88665cf05c460e85e44957318aa005:e9ed411860ed4f2ba0265705b8793d05]  AFAIK you wouldn't have the permissions to update or create a custom log file

Why  don't you create your own audit module persisting that information in DDBB?