@sudhakarj3480 From your question, it looks like, the dropdown values are displayed in alphabetical order but you want to display the values in your dropdown in some specific sorting order. To achieve this there are few options:
1. Have a column in the source table where you can maintain the sort order and and while fetching the data from the table use that column for sorting in Report Def.
2. You can sort the data after fetching from table as part of post processing (in DT/Activity) before pushing it to data page
There are other ways as well to sort data while displaying in a drop down. Pls check and try any of them, it should work.