Installing on MS Windows
For installation of the Helpdesk plugin on Windows, you need to install the Bitnami Redmine stack first. Please check this guide which will show you how to download and install the Bitnami and then the steps for installing the plugin via Bitnami.
Note: Please note that before installing the Helpdesk, you have to install the Contacts (CRM) plugin first because it is required for Helpdesk to be able to work. You can use a Free (Light) version, which would be enough for the proper functioning of this plugin.