Brugmansia, or angel trumpet, can be overwintered indoors in cold climates. They don't make very good houseplants, but the goal is simply to get them to survive until they can be moved back outdoors next spring. If your plant is not already growing in a container, dig it and pot it up using a good container soil mix.
I usually cut my angel trumpets back at this time of year. Depending on space available, they can be cut back to several inches or several feet above the soil level. I overwinter mine in a cool greenhouse (often gets to 40 degrees F at night). The cool temperatures keep the angel trumpet in a semi-dormant state until late winter, when temperatures in the greenhouse warm up because of increased sunlight and daylength. You could also keep the plant in a cool sunroom or other cool spot. Plants don't need a lot of light while they're semi-dormant, but once they begin to grow again, give them as much sunlight as practical to avoid weak, stretched growth. Wait to move the plant outdoors until temperatures are consistently warm. Angel trumpets need lots of warmth and moisture to grow and bloom well.