Perhaps your brother should have asked this question. He needs to state in his letter WHY he wants to do this. That isn't clear from what you've written here.
Is he bored/disinterested, etc. in the field of his current PhD work?
Why does he have such an overwhelming desire to study Environmental Protection? Is that his current field?
Is a PhD from Belarus not recognized in the rest of the world?
It's just hazy what his motivations are.
Please supply additional information.
Sorry, I will have to opt out. A family situation has occurred that I need to take care of this afternoon.
The question is open to all experts.
Good luck to your brother!
Sorry no one has offered a template for you. It is because you didn't provide enough information to write a good letter. Here is something you can start with:
I am currently a PhD student in (enter your field of study) in Belarus. I have discovered that my current credentials will not be recognized in most of the world outside of Belarus which will limit my choice of employment, and even impact where I can live and support my family in the future.
Transferring such of my credits as will transfer to Sweden and enrolling in a master degree program there in Environmental Protection will provide me with a broader education and the credentials will be recognized world-wide. Swedish education standards are top notch and I feel that I will gain a better education there.
(You can add anything you want here about WHY you want to change fields since you provided nothing.)