UPDATE (problem solved)
You need to modify the head.php file in the current template folder (in my case "delta").
In this file, change the url of the "cloudflare awesome font".
For example, I put this update version: (www)cdnjs.cloudflare.com/ajax/libs/font-awesome/5.15.3/css/all.min.css
The second step is to modify the /oc-content/plugins/online_chat/user/chat.php file by identifying the classes that contain the awesome fonts to modify.
For new font-awesom codes, use these codes: (www)fontawesome.com/v5/changelog/latest
Finally the last and third modification, is to modify this part of style css: oc-content / plugins / online_chat / css / user.css
Line 16 of the file must be changed as follows (in red, the modified code):
.oc-chat-in: after {position: absolute; right: 10px; bottom: 10px; color: rgba (0,0,0,0.03); font-size: 80px; width: 80px; height: 80px; line- height: 80px; text-align: center; font-family: "Font Awesome 5 Free"; content: "\ f086";}