Customers > Customer Newsletters-Add > Edit
From Shopnix Help
How to Add Newsletter Subscribers?
If you want to subscribe newsletter for the customer manually, then you need to follow below-
Go to Admin > Customers >Newsletter Subscribers > Add New Subscriber
Then you will get Add Customer Newsletter Page, fill the name, email id and click on Add button.
If you have more queries or would like assistance with this,please contact us on email@example.com.