How can I place objects over the surface of HDRI? I want my objects to be perfectly aligned with the HDRI as if the object is sitting on the ground. when I set an environmental texture to blenderworld, the objects float in the middle of nowhere. So I want to know, how can I fix this issue ?

as you can see in this image the object is perfectly lining up with the HDRI.
create a plane under your object and keep it as shadow catcher... Search on Youtube for Shadowcatcher