Simply click on the "My Subscribers" link on the left hand navigation, and when you get to that page, click on the blue "Add Subscribers" button on the right. This will take you to a page with three options for creating new subscribers.
Option 3 is "Import from you Seniorleads account". Enter your user name and password for your SeniorLeads account in the appropriate fields, and hit "Import". Any prospects you have recieved since you last imported your list will be added automatically to you eNewsletter subscriber list.