Hi,
I’m blocked with this. 
Case A.
I import a model obj that have the center misplaced. How I must place the gizmo pivot to have the symmetry working well?
Case B.
The imported model have the symmetry center fine, but I move some part of the model changing the pivot. How I must reposition the pivot to the center to activate the symmetry again?
Example of case B. Symmetry appear misplaced and no way to center it again… 
With out looking too much into this, how about throwing the grid on and in orthographic view usi g that as a way to centre the pivot?
G
In fact the pivot (in the image) is centered, but when enable symmetry remain misplaced
It’s not switching between local and world symmetry is it ?
Assuming your symmetry is set in World space (need more information… we can’t magically guess)
It’s centered relative to the mesh, probably not to the world origin.
Default symmetry setting is World, so you need to move your mesh in the world center.
Try gizmo → move origin (or better, reset in case your mesh is symmetrically centered in local space) .
Maybe this explanation will help you:
Vielen Dank @Holger_Schoenischka für die video, finally I find the gizmo edit, I can’t find it. 
Seems an experimental feature, this mean that will be disappear? I guess is very useful to recenter symmetry now I know how handle it. Thanks again for your help and your videos.
I’m here again
Why when I add a new mesh the symmetry is displaced??
In the following pictures the model is recentered the symmetry, then I add a sphere but the symmetry is where appear, so when I move it, the symmetry left displaced…?? What im doing wrong?
You are bound to have issues if you use it, because it means your model is not centered.
As for your other issue I don’t get it, explain better.
Try to display the plane as well, not just the symmetry white line (maybe there was an issue on the line display with the current released version, but I’m not sure)
Maybe try the web demo to see if the issue remains.
Ok, I will try again on the app and web
