Update: The question was partially wrong -- specifically in its assertion that ドゥ is a 拗音 (ようおん). The correct concept should instead be Small Kana. Please see Elrikr Utlendi’s excellent answer below. Later I also found this article on small kana. I've decided to retain this question as is because other Japanese beginners may come to a question like this via a similar mistaken route.
I can type most Japanese on Windows IME, but I am stuck with this one.
How can we type ドゥ or ドゥー?
It is used in this word (meaning "Hindu")
I know ド is
and ウ is
u, but here it is a smaller one meaning a 拗音（ようおん）-- a relatively rare one that is not shown on my text book (みんなの日本語)
Google Translate gave me this Romanji
which also looks very odd to me. I could not use this romanji with my Win IME to get the Japanese words
du, Win IME gave me づ
dou, Win IME gave me どう