I don’t think inability to express anger is the cause of anger! You will have to see why anger arises at all in the first place. Generally it is due to some kind of unhappiness or frustration in life, usually something one wants but is unable to acquire. I presume it has not been inherited or learnt within the family.Â
In any case one has to find why the anger is arising and address that. If it is due to some feelings of inferiority or something one wants to achieve but is unable to get it then one has to find alternate ways to move forward. It helps to read good books and listen to soft soothing music as it helps open the doors of mind to harmonious movements and refines the consciousness. On the other hand, excitement and impulsiveness, impatience, restlessness are close cousins of anger. Regular practice of Asanas and deep breathing helps here. Finally, as far as expressing anger goes it is much better to sublimate it through sports of your choice or vigorous physical workouts and activities such as swimming. Try these and see.
Affectionately,
Alok Da