flyrocky,
There is no conversion process. Your friend will have to obtain a license from scratch ie do all 13 EASA exams followed by an initial medical and flight test in the state of license.
At best, with the right experience, he can apply for training exempt status which allows him to just arrive and write exams without the need for formal ground school(some 650 hours). Same for skills test - just arrive and do a skills test without any ATO involvement.To find the experience requirements go to the website of his target country and they should have a process for applying for training exempt status. I speak under correction, but I think he needs to have a full ATPL(and it needs to be valid with a medical), so if he hasn't done the skills test in Bangladesh then he needs to sort that out first.