To move contacts from one list to another:
1- Go to the Contacts page. Find the 'Smart Filters' tab on the left of the page. Under 'Lists', select the list you want to move customers from, then choose 'Apply'.
2- Select all customers in the results pane by marking the checkbox at the top of the results.
3- Click on the List Icon on the top and select the destination list to move the contacts to.