how to set the moved bone to original location? I moved the bone in post mode but I want to reset what I have moved, I selected the bone and pressed alt + r, it's not working.  How can I reset the bone I moved? I can not undo it as there are too many steps in the history.

blender2.81
Go to pose mode, select the bone, and go to the search tab. Search "Clear pose transforms" and it should do the trick.