You wrote you were importing subscribers via a csv file.
When email adrresses are not present in your database it will create new records for them with all the information that is present in the csv file as long as you have matched the fields in the csv file with these in Acymailing..
If an email address already exists in Acymailing you get to choose if Acymailing should update the subscriber or if it should skip the details. This choice is made in the second step of the import by enabling or disabling the swith "Overwrite existing user's information".
If you need further assistance, please provide us with more details about what exactly is not working.
See also: https://docs.acymailing.com/main-pages/users/import