<< Is there a simple way to bring it vice versa

Use the mirror function ?

I redrawed but I still cannot filleting the relevant edges.
The script told me the filleting edges are not naked...no idea anymore...

Follow the Michael steps for build your object!

I guess I was pretty near to his suggestions.

Workflow wrong?
Gererally - is it the wrong operation to cut a geometry with a line or cube/boolean in order to get a spline? I split/cut/bool, then I mark the spline, copy and paste it - give it a name...and then the spline description points are so many?!
Is this wrong and may this be the issue for my bad modelling?

yes but your own model has some edges "segmented" for any reasons!

When you have such number of points for a curve (circle above) : Press TAB and write Rebuild for a reasonable number!

Hi Mala, there are some problems with the model, a couple of things I noticed were edges broken up into small fragments:



And some areas where edges are not meeting very precisely:





So yes your process here is not making optimal geometry.

re:
> Gererally - is it the wrong operation to cut a geometry with a line or cube/boolean in order to get a spline?

Well it depends on what you're going to do with it but if you're repeating these kinds of operations on splines through several iterations that's probably not so good.

I also noticed you have some "non-optimal" shall we say construction here:



It's odd that the surface has that slanted construction to it, it's better for the surface here to have a planar end and to have the slanted areas be cuts on it.

One of your other surfaces is set up like that but not this other one.

- Michael

Hi Mala, what is your construction method for this piece here? :



With it being slanted it would probably be good for it to be extended so it can intersect the other surfaces.

- Michael

I'm trying to figure out your design intent for that area, is it supposed to have a non-uniform shape to it? :



Or should that be an even surface of revolution (a piece of a regular cone) that is just rotated?

- Michael

I made this sweep:

I think I'm understanding that the design intent is for there to be even distance between the angled cuts and then that cone-ish shape is filled in between those.

- Michael

This is the new confusion base I begin from. I know this looks not very good...

The goal is the right object.
Left is the construction, then on the right side it is bended. (normally it is perfect in geometry)
The only thing is that the direction of the lower thinner part should be mirrored to the other side. That is what I asked some questions ago. This is the reason why the new drawing goes to the other side then before.

Previous question from Michael, answer: I cutted it out by a cube

Hi Mala, how about this attached version, is it correct?





- Michael

puh...I fear yes...and that you needed just 7andAHalf minute...?!
In order to test it I have to expand it. Is it possible without a seam?

My expanding result. Made with extrusion tool. I hoped to pick the points in order to move the border line. No points to pick...I do not understand such things. Sometimes you may see the points of surfaces or objects, sometimes not...

No...It has not the right direction...difficult to explain

Another Idea: Is it possible to redirect the direction of a spline in MoI?