To be able to add leads to an existing list or a new one, follow the steps from your main dashboard:
Add leads to an existing list
Go to Data Management
List Management
Use the search box to find the existing list
Select
Add Contacts/Leads
Scroll down the page
Tags -> add the tag used when uploading the file
Preview
Add leads to a new list
Create the list
Use the search box to find the list
Select
Add Contacts/Leads
Scroll down the page
Tags -> add the tag used when uploading the file
Preview