@pheijmans in order for the developers to help you you need to provide more details. Which icons are the ones too big? Can you provide a sample URL where the problem happens? What exactly do you mean when you say the plugin doesn't work?
Please navigate to Dashboard > wpDiscuz > Forms admin page, edit the Form and just click on the "Update" button. Then delete your website caches and press CTRL+F5 (twice) on the frontend.
In case you want to say thank you! π We'd really appreciate if you leave a good review on the plugin page. This is the best way to say thank you to this project and the support team.