Thank you for your tip. But imagine I have lost the original Shape then what is/are the best way/s to recreate the original shape out of the altered one?

As I mentioned I tried Swipe & Network which gave me a shape close to Original one but it is still not the one I had started with! I just wanted to know if there is a method to do so.

A simple way is :

select your object.
Edit/separate
Select the useless surfaces and delete them.
Select the main surface
Select all edges you want delete
Delete them....
The holes disapears !

And you have your original surface.

Don't forget to select and join the surfaces to have original object.

Dear Pilou,

I found a solution to my particular example :-)

It seems there are few tricks, My problem is solved thanks :-)

Edit:Dear Phiro,

Your trick was so handy and quick! Thank you so much! :-)