I think it is difficult to change our reactions without first at least some awareness around a) what types of things we are mostly over reacting to (i.e what are our main triggers) and b) the feelings behind the over reaction e.g. feelings of rejection, being forgotten etc. It can then be helpful to recognize where that feeling may have originated (but not absolutely necessary and doesn't need a big deep dive into the past) e.g my mother rejected me as a child, I was forgotten about alot as a child) This allows us to bring more awareness to the triggers then when it arises in the future. Developing an ability to recognize and then stand back from our reactions can be helpful. I think you mentioned he also worked alot with mindfulness LT so this may be a good route to try.

This is just one way that can be helpful I am sure there are also others that posters will share.