B32 shower drain

[Cat2]

I would like to reroute the  piping from the  shower drain on my  Bavaria 32 which will involve possble replacement of the original piping.
Does anyone know how to remove the original without involving destructive techniques?
No obvious screw  from the top; no access to fitting below.

Is it  possible that the  plastic grating screws into the lower part of the  fitting  and is tightened to make the seal?