If you're anything like me, that kind of anger can be pretty hard to access. Especially if you've had a lifetime of suppressing it already which most of us have if we learned pretty early on in life that "Mummy doesn't like me when I'm angry" :-)
I have a practical recommendation for anger, which is that, if you drive, you can use your car as a kind of therapy room. Letting off the kind of shrieks and moans, screams and yells that I do when I'm really angry just can't be done within the confines of a house, or where I think anyone else can hear me, so I get in my car and drive to a remote spot, then let it all out. And, if you can, tap whilst doing it too, even if it's just one or two points. Some good strong loud music can help too.
When you feel calm is a good time to make a list of all the beliefs you have around anger too, like it's wrong, or it hurts people, or you'll be told off if you show your anger. Then you can tap through all these beliefs until you get a clearer idea of what your anger is and how to work with it because it really isn't a forbidden feeling.
We are mostly taught to either suppress our anger, or to express it by hitting pillows or such like. But there is a third way which is to just feel it. Sit still or walk, whatever you need to do, and just feel and observe your anger. Out of that will always come right action, by which nobody is hurt.
It's the years of pent up rage and anger that needs to be let out first though, and if you thought you weren't an angry person (I actually said that to someone once :0) then I encourage you to think again - and to deeply and completely love and accept and forgive yourself too!
I do hope the healing is going well after your surgery.
Marian