How to Customize default error message

Hello there, I run a server and was wondering how I could edit the custom default error message with essentials. For when I type a command like /jk and it says 'Unknown command type "/help for help. I was wondering where I can customize that in the configuration so i can change it to 'Command not found' or something else that I wanted custom thanks for the help!

PS: I'm not good at any type of coding so i cannot do anything with the java code or whatever code.