Anger as a tool for self-awareness and self-knowledge
Anger is an indication that some desire, attachment or need of yours is being prevented from being fulfilled or unfulfilled.
Therefore, whenever anger manifests within us, we understand that some desire, need, attachment is being hindered, that someone, some situation or event is preventing our desire, need or attachment from being fulfilled.
So, you can use your anger to investigate and discover what desires, attachments or needs are limiting your mind and causing you to suffer and not experience freedom, happiness, love and peace.
The inner work does not stop at discovery, of course, but continues with investigating, understanding and eliminating anger as well as attachment, desire or need.