Answer: Alstroemerias prefer regions with relatively mild winters and not-too-hot summers.
You could have left it outside until frost killed the foliage. SInce it is already indoors, keep it in a bright but relatively cool spot (50-60F) and water sparingly, but don't let the soil dry out completely. The foliage should naturally die back and the plant will enter a dormant phase. Once the plant is dormant, cut back on water even more and keep the container in a cool, shaded place. When you see sprouts, move the plant to a bright location and increase waterking again. You would not need to transplant it unless it has become very crowded.
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