@sandeep1 There are a few ways to handle this. Generally speaking you need to pick up the file, parse the file, transform the file, and send it on. Part of the fun with NiFi is completing this task. My recommendation is to start with some known CSV examples. Get them working, then adjust them for your scenario.
If you reply with a sample of your CSV, and more clear idea of what you are doing I can provide a better example or a template. How are you going to get the CSV into NiFi?
Also your post subject, and the body conflicts: Do you want to do csv to lower case OR parse a column to get a different csv?