See if you can go back and forth (pendulate) between the tension in your back, and your intention of the kidneys softening and dropping down. Not like they have to battle it out, but more like both are options to consider. Notice the tension, then focus on the kidneys and the surface under them, back and forth. It may be helpful to put something warm under the kidneys, to increase the sense of safety and support there, like two hot water bottles about one-half full, or a heating pad.