now…the pivot is in the middle of the gameobject.how can i change it to top left?
Inside the Unity editor, you can’t. If you only need to temporarily rotate the object around a certain point, then you can palce an empty gameobject at this point, and make it a parent of your original gameobject, and rotate the parent.
If you actually need to change to pivot position and orientation, then you have to do this in a 3D modelling application, like Blender or 3D Studio Max.