Changing Service Icons

Hi! I need help changing the service icons on the home page! In other themes I have used, those are changeable by clicking a dropdown box in the Customize section, but that doesn’t appear to be an option with this theme (or it doesn’t seem to be working.) How can I find a list of accepted icons and their names/codes to replace the default ones?

Thank you so much!

The page I need help with: [log in to see the link]