Sorry,
Your question too vague,
you can get the list of label of mesh3 Th
int[int] labs = labels(Th);
cout << labs < endl;
or you can build the surface mesh
load “msh3”
laid “medit”
Th = buildBdMesh(Th); // build the surface mesh
meshS Th1 = Th.Gamma;
plot(Th1,wait=1);
medit(“Th1”,Th1); // to see label of region of Th1 …