Did you have DC taxes withheld? If not, delete the DC return or just don't mail it.
DC has reciprocity with each state. Simply stated, nonresidents who work in DC don't file taxes with DC. The only reason you would file with DC is if: A/ you lived there or B/ you had DC taxes withheld in error
If you had DC taxes withheld in error, and need to get them back, mail the DC (D-40B) return to:
Office of Tax and Revenue
PO Box 96147
Washington, DC 20090-6147