If your bot has an avatar, it will display the avatar's image or video. If the bot does not have an avatar, then it will display its icon image.
I assume your bot has an avatar, so you can clear this by going to its Admin Console, Avatar page and set the avatar to blank and clicking Save.
To set the bot's icon image, click on its image on its page, or click "Change Icon" from the menu.
You can also create your own avatar for the bot with the image. From the bot's Admin Console go to its Avatar page and click "Create". Then in the avatar editor upload the image.
If you are using the Julie app, you need the first upgrade to Bronze, create your own Julie bot "Chat with My Julie", then from the main screen menu select "My Bots" or "My Julie" and select your Julie bot. Click on the bot's Admin menu/button, then click on Avatar, and click on Create, and upload the image.