Can someone please help me to make a background which is repeating after some time.
Like I have a main background of space and I want to add planets and some other things for the background and want to repeat them after a particular amount of time.
So please help me out in its script
Well, there are a few ways for this. Firstly, you can reposition the object by changing its position values via code. It would be something like gameObject.transform.position = new Vector3(400, 200, 0);
Or you can instantiate another object with pre-determined positions. For that, you need to save your current planet as a prefab and Instantiate it by code. These links would help you:
look up changing the skybox.