You can upload the contacts that are on your DealPOS to MailChimp when your DealPOS and MailChimp have been integrated. For example I choose contact with name "Dahla"
1. Go to Upload-Select join date-then click upload
2. You have successfully Upload contact to MailChimp
Note : Here's tutorial for create new list : https://kb.mailchimp.com/lists/growth/create-a-new-list?_ga=2.153189374.715086048.1520231547-874212655.1520231547