I am not a doctor or physical therapist. It may be wise to consult your doctor or physical therapist before doing any stretching exercises. The stretches in this video have worked for me, but we all have different bodies and not all exercises are appropriate or advisable for everyone. This is especially true if you have any pre-existing conditions.
Go slow. In the beginning, keep sessions short. Pay close attention to the sensations in your hands and stop if you feel pain.