you cannot alter the data that exists.Crystal reads data it does not edit data.
You can create a formula field to add to your data set and use existing data to derive a value that is unique per row.
Also do not put these types of fomrulas into the select expert. The select expert is how you select or filter out specific rows or groups of data from your data set. BY putting your current formula into the select expert you are basically evaluating each row for a T/F answer to your formula which is always returning a false, thereby excluding all rows of dta from your report, hence no results.
In the field explorer create a new formula field called "updatedQty" (or whatever you want)
IF ORDER.TYPE = 'SOI' THEN ORDERQ.QTY ELSE ORDERQ.DLVQTY
Place the formual field onto th detail section to see if you are getting the value you expect.
Remember though you did not alter DLVQTY, you just added a new "field" that is executing the formula to get a result.