This section will show you what to do when the scene becomes dark during placing the assets.
It may be caused by the deletion of the Directional Light which acts as the light source in the scene.
To solve this problem, we have to add a Directional Light into the scene again.
Go to Assets > 3D Model > Directional Light.
Then light got into the objects in the space.
Look at the hierarchy and confirm if the Directional Light is added or not.