Firstly, pick your battles.
If it is something worth fighting for, speak up. That doesn’t mean get into arguments. Before you speak, have your thoughts in order. State your position when you know how you want to say everything. If it is a situation where you can support yourself with documentation, have that ready.
If it is not worth speaking up about, make peace with yourself.
Look at yourself from within, outward. If the planet were to explode right then, is this anger something you want to have with you your very last moment of life? No. So shake hands with it, say, “nice knowing you” and send it down the road. Don’t let it build a nest inside of you. It is junk. Think of yourself like a home. Do you want stinky junk cluttering you inside? Of course not. So, mentally picture the problem packing a suitcase, and heading off to the airport.
It takes some practice at first, but it gets easier after a few tries.

You can’t not be angry if there’s some injustice and you’re being dominated by those with greater social or economic power.

Stop trying to blame yourself or fix your emotions when the factors are outside of you. Fucking vent that anger and do something about the things making your angry.

Physical exercise might help controlling your anger.

Understand where is stems from in the first place.
Somewhere in your past you felt subjugated against your will and thus every time a situation such as this reminds you or that first time it brings up a well of anger inside you.
Ask yourself if this is right for you? Is this job, this boss this person , this decision is right?
perhaps you need to ask why something has to be done this way etc?
Explain that you want to explore other ways of completing a task and in doing so you look at problems creatively and thus may come up with a better solution. You want to be involved in the solution process. Explain that to whoever you are having the problem with.
You are letting them know that you are an individual that requires input and respect for that as well.
If one constantly rolls over and complies then its a problem of not getting a word in. In a relationship regardless of work, or other it is the union of two individuals not one being subservient to another that works best for the group goals.
Also ask yourself why anger is the first response? Ask why something is decided on without your input? If it is a structured environment where things were always done this way, then perhaps its not the right place to work in?

Perhaps meditation or anger management classes. At some point your anger will turn inward and you will just be bitter and that can eat you alive.

May we have an example of the kind of thing your boss or family member might ask you to do that makes you angry?

Let yourself feel the anger in a safe place (like home). Stand in a room legs hip distance apart, ball you hand in a fist, and imagine that you are giving your boss (or whoever) a sharp elbow jab. Take your arm and shove it backward hard and say (out loud) “Get off my back.” Repeat several times. Alternatively, or in addition, put a pillow on the floor in front of you, and hit it with your fists (pummel it hard) and say (out loud) while thinking of the person you are angry at “Take that.”