 So, you don't know how to mirror objects in ZBrush. Not a problem. Now there are two types of mirror options. If you go into defamation and mirror, it will keep the shape the same, but swap its direction across the X, Y, or Z axis. You can also mirror across multiple axes at the same time. The second technique is under geometry, modified topology, mirror and weld. This forces the right side to copy the left, and again you can do it across the X, Y, and Z axis individually or simultaneously. Hope that helps and as always I hope you have a fantastic day and I'll see you around.