Currently you can only choose between the icons we are providing. However, it is possible to use a custom image. To do this you basically need to follow these steps:
If you download our customer portal from Jira you have a packaged file called something like jsm-portal-app-2028xxxx
Open the file and you will find a color.png
Simply exchange your desired image/icon with this file but name it “color.png”
Upload the app/update the app in your teams admin center
Please be aware you need to have the same pixel size otherwise it won’t show up accordingly (193x193x).