just check the faq page of zipp.chat
You will need two images ready, an online and offline button. Following formats are allowed to upload png, jpg and gif. The buttons need following names: yourname_on.png and yourname_off.png. It is important to have it named like this or it won’t work, yourname can be a name of your choice.
Now go to your Zipp.Chat console and load the buttons section. On top you will find two input fields to upload your button, always upload two buttons at the time. Make sure you have the permission to use the buttons you upload.