Your first guess is 2. Assuming you’re not correct, I had 1, 3 or 4. I must change to 2, 3 or 4.
Your second guess is 3. If your guess was incorrect, I was at either 2 or 4 and so must change to 1 or 3.
You guess 3 again. You either guessed correctly or I was at 1. I must now change to 2.
You guess 2. Checkmate!
By symmetry your guesses might have been 3,2,2,3 instead.