You could select a large face af green part....create a sketch on it....convert the face in sketch and then use "Extruded Cut"
Or you can use the same method you used to create the green part but instead use "Extrude" you use "Extruded Cut"
you can use combine command too:
Thanks for your answers!
I tried the combine command but it cuts of from both elements.
The best thing seems to use sweep cut using the sketches that i used to create the green element, followed by sweep using the same sketches.