Can misalingment of one eye due to myopic anisometropia be treated only with eye excercises? How much improvement is seen?

NO. Anisometropia means that there is a different measurement of the need for glasses between the two eyes. Myopic - indicates that you are nearsighted. There are no studies that would indicate you can change the condition with exercises.
Eye doctor can help. A visit to one or two pediatric ophthalmologists can offer opinions on the best ways of treating it. Haven't heard of eye exercises being of help. The doctors will likely have to decrease the myopia in the bad eye, by such methods as contact lens, laser surgery, etc...