You've been able to add your own icon to any app on Bitrise for a while on the app's Settings page (instead of seeing the first and last letters of your app's name on the dashboard), but from now on you can fix up the icon when you are adding an app to Bitrise.
You can either choose one that is already in your repository...

... or you can upload a custom image by clicking on the + sign.

Select the image and then proceed. And that's it, you'll have an icon displayed on your dashboard:

Or, if you select Skip for Now during the setup process, you can always add one later. Go to your app's Settings tab, then click on the default icon (SD for me) and add yours.

Oh, did you know that you can also set profile pics for your profile and your orgs too?
Happy building! 🤖