hi Irina, sure you can heal your knees with dry fasting but it will take time.
my knee problem is caused by dry fasting sort of , I think. My regular dry fasts heal the wear and tear in my knees but every now and then it will get worse before it gets better, I had a similar problem with my hips a while back.
I think it is healing a previous injury in my knee but still hasn't finished, it still hurts a bit so I need to do more dry fasting to finish the job.