We're still working on the Help Scout integration with Retently and it should be launched anytime soon.
If you want to import your customers manually, please read this information provided by Help Scout:
"All data within your Help Scout account can be obtained as needed using one of our APIs. Exporting data via the API is currently the only means of obtaining data. We're working to add more user friendly export options within the Help Scout interface.
Help Desk API
Customer and conversation data is available on demand via the Help Desk API.
All Docs articles can be obtained using the Docs API.
On request, we're able to provide a .CSV file containing the names and email addresses of all of your customers."