This feature gives you flexibility to create and target user segments you have identified through some user analysis at your end. You can upload and import a list of users containing one of the user attributes to identify that user and a custom segment containing those users will be created.
Step 1: Go to the Custom Segments tab on the segmentation page
Step 2: Select the User Attribute your list is using. Select a file, custom segment name & provide an email where we can let you know once the segment is created.
Note if you don't see the segment after getting the email, just refresh the page.