This reminds me of that old joke about economists. If you put 10 economists in a room, you'll get 11 opinions...
Everyone will give you an answer based on what works for them. So find what works for you. You are the person behind the trade; pulling the trigger, therefore your solution to the mental game will be personal.
Lots of good suggestions... But for me personally:
First and foremost Mark Douglas. "Trading in the Zone" transformed me from a mental wreck to a professional trader, that and a lot of help behind the scenes from a couple of very important people here on ET.
Secondly I found Jared Tendlers "Mental game of Trading" to be of enourmous help. I tell people that I've helped that Mark Douglas tells you what is wrong, Tendler tells you how to fix it.
Couldn't recommend these two books highly enough. They help you to develop a probability based mindset, and give you a framework to continually assess and improve.
As Douglas said: "Trading is a pattern repetition numbers game"... The rest is repetition.
There are practical exercises you can do to imprint a probability based mindset, reach out if you want more info on that.
Finally, as an aside, I found a few points in "Thinking in Bets" by Annie Duke useful as well...
Good Luck! The rewards are there if you put the work in
/fin