The following solution works in this case, but may fail with more complex meshes.
First you would have to define somehow where the inside and the outside is.
You can do this by using the node
Attribute Statistics to determine the center of the geometry.
By subtracting the position of the individual points of the mesh from this position, you get the direction vector to the respective point.
If then the dot product of this direction vector and the face normal is greater than $0$, then the face is obviously pointing in the wrong direction:
In your special case, however, you can use this technique, but you would have to apply it at a different place in the node tree.
Since you have two different objects here, which you process with
Mesh Boolean, you would have to compare the normals of each of the two objects with those of your additionally created mesh and apply them with
Something like this: