Handle 3D object in 2D scene and AR scene

I am making a game which allows users put a 3D model in 2D scene. In that scene, I have a button to switch view into AR. I touch in plane and place object on it but the size of object too large. If I modified the size in the prefab, object will be too small in 2D scene.
How can I solve this problem.
Thank you in advanced

Scale the ARSessionOrigin object. Here is a good explanation: