The following guide will teach you how to completely remove the plugin from Redmine. You have to follow these steps:
Downgrade your databasePlease navigate to the Redmine directory and execute the following command:
bundle exec rake redmine:plugins NAME=redmine_contacts_helpdesk VERSION=0 RAILS_ENV=production
Delete the plugin's folderTo do so, please execute the following command as still being in the redmine/ directory:
rm -fr plugins/redmine_contacts_helpdesk
Please restart your web server.