We strongly recommend that you work with the PEO to find the right person to coordinate with in the office of legislative affairs.  The liaison for your PEO should be able to assist you in this situation.  On the Financial Management side, normally a Congressional Add gives specific directions for the effort/task that the appropriation funds are being added.  I would ensure that you have talked with your Business Financial Manager to have a complete picture of the task/effort of the Congressional Add.  See this link for further information on the Legislative Affairs Office https://la.defense.gov/ - "The Assistant Secretary of Defense (ASD) for Legislative Affairs (LA) is responsible directly to the Secretary of Defense for maintaining liaison and relationships with members of Congress and the Executive Branch. In carrying out these responsibilities, the ASD heads a staff of managers, action officers, and support personnel, who manage, control, direct and monitor communications and activities involving Congress and elements of the Department of Defense (DoD), including the Office of Secretary of Defense (OSD), Joint Chiefs of Staff (JCS), the Armed Services, and Defense Agencies"