Follow the below steps:
1. Create calculated fields to a group of n depending on years.
2. Create a parameter for selecting the current year.
3. Now create another calculated field to check current year vs previous year as if the order date is equal to the current year -1 then the customer is an existing customer else a new customer.
IF YEAR([Order Date]) = YEAR([Current Date])-1 THEN "EXISTING CUST"
ELSE [Customer ID]
Hope it helps you.