There is a customer database, you can choose change customer from the overflow menu on the top of the check details and enter a new customer or lookup but it requires a phone number to enter them. If that doesn't work for you another option might be to use a menu group and menu items for member names, just make a menu for member names, with the names as menu items with no price, you could organize with groups based on alphabet A-E, F-J, etc. if you have a large number of members. One downside to this is the names would be included in menu reports.
