I am a medical doctor and I want to study abroad inn the field of HIV/AIDS with the help of a scholarship.

I don't know about free training but
These two organizations are volunteer where you could have on the job training
But I don't know how much they deal with HIV/AIDS

MSF-USA: Doctors Without Borders

Los Médicos Voladores: Volunteers

If you can't find what you are looking for you might want to consider one of them.