Hi Mala, it starts with the file you posted above, "hand Moi Forum Shown.3dm".

Open that file and select this surface:



Then run Construct > Curve > Silhouette:



In the command options choose "View: Top" and then push "Done" :



That will generate these curves:



Just these 2 are used, you can delete the others:



Then it's Trim the surface by those silhouettes, Construct > Curve > Project to project the silhouette to the construction plane, then you can either loft between the silhouette and projection or extrude the projection and trim it. Let me know if you need more step-by-step for these parts.

3dm file attached.


- Michael