DC has Congressmen, but not Senators as they're not a State.
Congress can add a state without a Constitutional Amendment, but as DC is a Federal District mandated by the COTUS, an Amendment would be required for it to gain statehood.
That said, we're already beyond the COTUS scope for DC. The District is supposed to be under the authority of Congress, not a local government and is not supposed to exceed 10 square miles. It currently sits at something like 60.
I don't really understand the point other than trying to add another 2 virtually guaranteed Dem votes to the Senate. They're already represented in the House and the District is already self governed instead of being governed by Congress.