Q.how to ripen red bell peppers
Due to the weather, we had to pick all of our peppers before they were ripe. All of our red and yellow bell peppers are green. Should we sit them in the sun of the window sill, or should we place them in a paper bag or other dark place? Will they turn from green to yellow, orange or red or will they remain green?

Based on my research you can get them to ripen red by storing them in a box in a dark room with temperatures between 65-70 degrees for a few weeks.
For more information on growing red peppers, please visit the following link:
https://www.gardeningknowhow.com/edible/vegetables/pepper/how-to-grow-red-peppers.htm