This to add imported contacts to an existing list
If you have successfully imported contacts and you want them to add to an existing list.
After the upload:
1. Go to your uploaded list (make sure that in the process of import, you didn't created a new list for that set of upload), then select More.
2. Then on the drop-down list, select Add imported contacts to list.
3. Select the list you wanted to contacts to be included to, then select Add.