Do you have a D major chord?

The notes for a Bm chord are B-D-F#.

The notes for a D chord are D-F#-A.

Hold down the D bar, check at the base of the autoharp to see what the notes are on each string, and pinch to get as many of the D and F# notes as you can without hitting the A strings. As long as there's another instrument sounding the B note, it'll sound OK, even if the autoharp itself sounds a bit thin. It's not as hard as it sounds, and it's something you need to learn to do as you get better on the autoharp anyway.

You can try a similar work-around with the E7 chord, which has notes E-Ab-B-D, by just playing the B and the D notes. It's a little harder because there's two note to avoid, the E and the Ab.

Good Luck,
T.J.