When you complete the "kicad to Ngspice converter (Ki-Ng)" step in Oscad, by default it generates Scilab compatible netlist also. If you see the terminal output after "kicad to Ngspice converter (Ki-Ng)" step it says you about the scilab netlist generation. You can find this netlist file in your project folder and it's name would be your-project-name.cir.ckt.