The Washington DC forms have not been released yet; this means that the
forms and the programming behind them (and the testing) are not yet officially
available.
If the state is released and the entry for the credit is not there, then
come back and make a comment.
The expected release date for DC for Online is 1/31/2019, but you can check
the status at https://ttlc.intuit.com/replies/3319879
