Possible ways:
1. If you use a standard field "Address", just right click on the field and choose: "Edit the field properties for this field". You will see "Address field options", where you can find "States" . So , just change the full name of these states to the abbreviation, like New York - NY, California - CA.
2.Second possible way- write a formula. Add a new Text-formula field . Call it "Abb"
If ( [State] = "New York", "NY"; ....) And write states what you need. And in the future, just use this field in your reports.
Have a good one!
