You can select your own card that was taken by your opponent with “Exchange”. The card returns to the owner’s deck (yours, in this case).
GoatRulings.com Rulings:
Q: If I activate “Trap Dustshoot” when my opponent has 4 or more cards in their hand, but an effect is activated (such as chaining “Book of Moon” or “Mystical Space Typhoon”) after “Trap Dustshoot” is activated that causes them to have less than 4 cards in their hand, do I still get to see my opponent’s hand and return a monster?
A: Yes. If a player has 4 cards in hand when “Trap Dustshoot” is activated and they chain a card causing them to go below the 4 card requirement you will still get the effect of “Trap Dustshoot.” For the player to successfully dodge “Trap Dustshoot” they would need to use their turn player priority to use “Book of Moon” or “Mystical Space Typhoon” BEFORE you activate “Trap Dustshoot”.