We are not able to install HelpDesk unless scripting capabilities are enabled.
If you use a SharePoint administrator account to install HelpDesk, scripting capabilities will be enabled automatically during installation, otherwise, please ask your SharePoint administrator to install HelpDesk or to turn scripting capabilities on manually. For detail see this MSDN article.
Note
When you install HelpDesk to Office365 Group site, this site will not appear in SharePoint admin center. SharePoint administrator can turn on scripting capabilities by using this PowerShell command:
Set-SPOsite <SiteURL> -DenyAddAndCustomizePages 0
Please note that you need to install SharePoint Online Management Shell.