Bypass new computer set-up program

I have a brand new iMac and am unable to access my wireless network, two different neighbors' networks, my iPhone hotspot nor a guest network. How can I bypass the new computer set-up program and resolve my problem? Yes, all packaging film has been removed and there are no reported problems with the ISP -- The network works fine with iPhone and another device. My Apple Support person, Steve, suggested a find an ethernet cable. Any other suggestions.