Sorry about your hand. Switching right to left is pretty impressive. Anyway, have you tried using your pinky (instead of ring finger) to fret the 3rd fret of the B string?
Or you can try an alternative voicing (fingering) of the D minor chord. The note that you're having trouble reaching on the B string is a "D", and you are already playing another D when you play the chord (i.e. the open D string). So if you use your ring finger to simply mute the B string you will technically still have a D minor chord with a slightly different tonality.
This GuitarTricks site has some nice reference tools that you can access from the home page by clicking the "Toolbox" button. This includes "Chord Charts" that illustrate alternate voicings for most chords. Here's the page that shows multiple ways of playing the D minor chord.
Man, I just can't get over thinking of how difficult it would be to retrain myself to play opposite handed. Heck, I have difficulty using kitchen utensils with my non-dominant hand 😄
Sascha
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