I want to rotate my image by a given angle.

I don’t actually get this concept of rotation. Does it happen about the origin? or about the centre of the image? Which coordinates?
Which transform should I use for rotation when I have only angle of rotation. and my image is a label map with only one large object in it.
What I want is, when I rotate, only the object alone has to rotate, it should not change its location

Most ITK transforms have center of rotation property, which is coordinate origin (0,0,0) by default. Frequently, center is the only fixed parameter. You probably want to calculate center of your object, and set that as the transform’s center.