Hello friends How to remove "Powered by EvNix" using a custom version? Eu pesquisei no arquivo client/freichat.js mais não encontrei a frase pwdby nem evnix.

You cannot remove the powered by attribution, it goes against the license terms. please read the license which has been provided in the zip file.
you can buy a commercial version if you are interested in removing the branding. you can request for a commercial version using the 'contact us' link.