How to rearrange the center point of a certain object in blender?

Question

3D

And also there is another question. Why when I move one object everything moves. sometimes not. I didn’t really understand, since I’m just going through the course and I didn’t need to move anything, but now I need to. But there is a peculiarity.. by selecting everything in the edit mode, I normally interact with the object. also when I tried to bind two objects (donut to icing), as a result, when moving along the z axis, the icing went into the sky faster than the donut itself. it separated, and without establishing any connections, everything moves together and evenly. the fact of the matter is that EVERYTHING is material (the camera and the light do not move).
Most likely I did not notice some more details. and I probably didn’t finish something, but I hope you remember something ....