All activity types come with a default icon to show on the platform. However, we can imagine that you want to personalize your platform and adjust some of the icons.
You can do this per activity in the activity settings. Go to "Content" -> "Activities" -> Open your activity -> "Customization". There you'll find the option "Set custom icon".
You can also add a custom (sub)menu item via "Features". Here you can enter one the icon names from below.
Available icons
Here is a list of all available icons + names: