If a chord does not exist in FastChords' repertoire but you know the notes to play (for example if you have the written music), then switch to Melody mode and copy the written notes, one at a time, and convert each to non-melody note with the convert button.  See Converting Melody Notes.

You might also send us a note, and we will include it in the next release of the chords dictionary.  You may then check for updates to retrieve the new chord dictionary from our servers.  See Checking for Updates.