how to train our brain to always use left part for thinking & deciding things? how to train our brain to always use left part for thinking &amp; deciding things?
How do I not take emotional decisions
Unfortunately this question is based on a false premise. Thanks for asking. The oversimplified view on brain lateralisation is so stubbornly persistant and it invaded so many meditation guides, self help blogs, pseudoscientific faith healing and even job interviewer criteria, that it is now a part of "viral" phenomenon. 

Yes, brain lateralisation exists. But it does not work in the oversimplified way they describe. 

Interestingly, M. Gazzaniga shown sometimes the "random versus linear" relation work in sort of [opposite][1] way than the popular myth. 


  Writing an overview of the split-brain research in a 2002 article for Scientific American, Gazzaniga concluded, based on the interpreter phenomenon and other findings, that the left hemisphere is “inventive and interpreting,” whilst the right brain is “truthful and literal.” This seems at odds with the myth invoked by Rabbi Sacks and many others. 


[1][https://www.psychologytoday.com/intl/blog/brain-myths/201206/why-the-left-brain-right-brain-myth-will-probably-never-die]