Fact: To join the military you need, generally, to be a citizen of the country in question. If you're Bangladeshi then that's your first port of call.
However, some countries do occasionally offer training to citizens of their colonies (eg. New Zealanders and Canadians in the RAF) but you have to have the right credentials and aptitude.
I would first ask the question of the Bangladeshi Air Force and then focus your attention in that region.
I wouldn't hold out any hope though
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