I still have the D.C. First-time Homebuyer Credit, but no longer have the home.

Even if you no longer own the home that qualified you for the D.C. First-Time Homebuyer credit, you may still claim the amount of credit you didn’t use on future tax returns until you have claimed the full amount that you are entitled to. 

Go to this section in Credit Karma tax: Carryforward of District of Columbia First-Time Homebuyer Credit

You can find the amount you can claim this year on your previous year’s return on Form 8859, line 4.