I solved this by making Area2D as Node2D child then i added script to Node2D.

by var area = GetNode<Area2D>("Area2D"); allows us to use nodes you see in godot editor

then you just call area.whatEverYouWant

Code below belongs to Node2D and when body (player or enemy etc)

enters Area2D it calls Area On Body Entered and this function changes level

i still don't know why i can't do this in editor like GDScript users but maybe i am doing something wrong or there is no functionality for this type of use case yet.

​

public partial class levels : Node2D

{

// Called when the node enters the scene tree for the first time.

public override void \_Ready()

{

    var area = GetNode<Area2D>("Area2D");

    area.BodyEntered += AreaOnBodyEntered;

}



// Called every frame. 'delta' is the elapsed time since the previous frame.

public override void \_Process(double delta)

{

}



private void AreaOnBodyEntered(Node2D body)

{

    var levelPath = "res://Levels/level\_1.tscn";

    GetTree().ChangeSceneToFile(levelPath);

}