If you have the camera that you took the photos with, take a photo with the lens cap on for as long as you did your other shots. Then you specify the shot taken with the lens cap on as your dark frame file. Rawtherapee then will subtract from your other photos the sensor noise. The dark frame photo doesn't have to be taken the same day. You could take it now. Doing it this way worked real well for me taking long exposures of fireworks. My 7d has some bright red dead pixels when doing long exposures.