Logging columns

Nextcloud version (eg, 12.0.2): 13.0.0
Operating system and version (eg, Ubuntu 17.04): Ubuntu Linux 16.04.1
Apache or nginx version (eg, Apache 2.4.25): Apache version 2.4.18
PHP version (eg, 7.1): 7.0

What file do I need to modify in order to change the “App” column to a “user” column in the logging section of nextcloud?