You might just consider retopologize the mesh? I dont know when your deadline is, and if you know how to retopologize. But I can assure you that learning the topology within zbrush wont take you more than a couple of hours. You could also try the “reproject higher subdiv” in the “tool - geometry”.
If you should want to retopo:
Just load your mesh, then open/press the zsphere in the tool section. When the zsphere is loaded, go to “tool -> rigging” and select your mesh ( the one you need to retopologize ). Then go to “tool -> topology”, and press edit topology. Now you can draw the new topology over the mesh.
When you topologize you’ll use “add point”, “delete point” and “move”, not really complicated. but you might wanna search for face topology to see how the lines should go. When that’s done you might wanna use “tool -> projection” to get your details onto the new mesh, before you go to “tool -> adaptive skin” and press “make adaptive skin”.