raph.zanin, the icons are not updated by just adding the Icon library app. The changes should be done manually, so you first add the Icon library app, then upload icons into the app, next select an element (e.g. geofences), and finally apply a new icon.
Icons, that are uploaded into the Icon library app do not delete the default ones. The default icons should still be available from the geofences' settings. However, I assume that the request is to restore the old icons that were accidentally replaced via the Icon library app.
That is a completely different question. Did you do the changes for different geofences from different accounts/resources? Did you do the changes at the same time (e.g. by selecting all geofences at once)? When were the changes approximately preformed?
You can restore the previous settings via the option «Restore content». Open an accounts properties, that you want to restore icons for. In the General tab find the button to restore the content. Open the menu, select a date and switch the restoration option from Replace to Merge, then select the required geofences and click Ok. After that, the system should revert the changes and restore the icons and other settings of the geofences as per the date you selected.
Restoring Resource Content — https://wialon-help.link/139b6a0c