Ok Lets start at the beginning. Did it ever have a Z motor installed or are you buying one to put in? Have you any experience in CNC and electrical wiring and troubleshooting so you would be able to figure this out? If the answer is NO do your self a big favor and contact Amazon for a Return under the A-Z Policy you have 90 days.
I have been a controls electrician since 1962, had some experience with CNC since 1994 or so. I can fix my own machines. But return the machine and look at Rabbit Laser USA Ray Scott sources and sells good machine with USA support. LightObject dot com, and Boss Laser also good Chinese lasers that work and have US support.
Yes, you will pay a few thousand more for something that works. Otherwise you have an ongoing project and you will dump a lot of time and money into.....