Depending on the terms and conditions of the UOC you are using, IF you are able to book a dining plan you will need to call to book a ticketless package since you already have tickets. It cannot be done online. It will be a package with all the rules of a package ($200 deposit, final payment due 30 days before your arrival day, applicable fees and penalties for any changes made to the package especially within 30 days of arrival). If you add the dining plan within 30 days of arrival it will have to be paid for at the time you add it.