Hi Sylvain,
I would search your configuration file for any remaining items from your iApp and delete those items. Remember to make a copy of your configuration file prior to making changes in case you need to restore. Their are a few free SCP utilities out their, including winscp, if you happen to be using windows. The file you will need to edit is bigip_conf and is located in /config/.
You can also use grep at the cli to make sure all your iApp objects have been removed. Something like
tmsh list sys recursive | grep "iApp" where iApp is the name of your iApp.