The way I do it is use a small towel or rag, put some conditioner on it and then rub it in the bag, starting at the bottom, front, back, sides. I reapply the conditioner on the same spot on the towel as needed. After everything is nice and dry, with a soft cloth you buff it out. Then you spray, nice and evenly. After 30 min, spray the second coat and you are done.
Always test on a small area, just to be on the safe side. I have conditioned the taupe, ocean blue and salmon color. No change in color, spray will darken it but it will disappear right away as it dries. Conditioning will make the bag patina faster.
Hope this helps.