With this latest launch, admin can Import reward customers manually from the admin end as follows,
Click on the Customer and the Reward/Product customer from the left side menus
Click on Import CSV button and then click on the Download Sample CSV button as shown in the image below
Sample CSV will look like this, refer to the image below

In the CSV file, admin add the customer details in the same format given and save the file to the local
Then again go to the Import section and choose file to upload the CSV which you have created
And click on Save to add the members to the list