I was wondering which way is the best to check if the set of surface in the model are flatten or not,
one quick trick should just to type sel planar srf, so I know those should not be planar, other ways ?
2-so how to rebuild it as planar srf in the most similar way ?
If you need to rebuild/edit any one of those surfaces as planar you can:
Set your Cplane using the To Object option, and clicking on any one of those surfaces you want to fix.
Select the surface
Use SetPt, and then select only Z, and use the Align To Cplane option.
You can either enter 0 for Z, or just click on a corner of your plane.
That will put all of the points of a surface into a planar relationship.
ETA - You’ll need to redo your Cplane for each surface you tweak.