This is the Unity forum, not the Unreal Engine forum. If you have questions about UE4, you are unlikely to get answers here. If you want to work with height maps in Unity, this might be helpful.
sorry, I made a mistake in translation Please tell me the method in Unity that uses png image as height information for terrain.
Unity needs a .raw heightmap file for terrains. Most external terrain softwares (e.g. World Machine) can export those. Or are you talking about this height mapping (parallax mapping)? https://docs.unity3d.com/Manual/StandardShaderMaterialParameterHeightMap.html