You get an extra 180 days to file and pay your District income tax after you return from service in a combat zone or a contingency operation. A spouse filing a joint return with you gets the same extension.
There is nothing to file in advance. File and pay within 180 days of returning. If you need more time beyond that, submit an extension through the MyTax DC portal, under Forms select Submit an Extension.
Your orders or Leave and Earnings Statements showing the combat zone or contingency operation service dates and the date you returned.