Customizing your bot’s chat button will help you ensure that your bot is easy to access and fits within your branding guidelines.
Keep in mind that the chat button should be a visually familiar icon that’s easy to find. You can do things like change the shape of the button, add text or a custom image, and change its background color.
In the Chat button drawer, select your preferred button style, and then further adjust its appearance. As you make changes to your settings, the preview updates on the right side of the screen.
Round button 
Click Default to just have a speech bubble on your chat button.
Click Custom Icon to upload an .svg file to appear on your chat button.
Text button 
Click Save Changes.
If your bot is live, the changes you make to your chat button appear immediately to your chatters once you save them.