Thoughts are as much outside of your control as they are inside of your control.
It works very much the same as breathing.
When you’re conscious of your mind or breath, you can actively control them.
But, when you’re no longer conscious of them, they carry on without you.
This is why you can’t just demand your mind to start producing better thoughts.
That would be like demanding your lungs to start delivering oxygen better.
You have to improve the thought-producing machine as you would the oxygen-delivering machine(s).
Which doesn’t happen after one exercise session (for either).
It happens after many.