Step1. Open Zbrush , Take a sphere, make it polymesh 3d and test whether the undo
(CTRL+Z) and symmetry is working.
Step2. Now go to Zplugin click SubtoolMaster - click - MultiAppend and then Select your
Zbrush file (.ztl) and delete the sphere which u don’t want. Now you can use CTRL+Z
and symmetry
Hope this helps
Cheers