It sounds like he just wants an adaptor (just 2 connectors and some wiring)
If this is the case.
The first program you open from kicads launcher is the schematic editor.
Once in there on the right hand side. Third button from the top is “add component”, you will want to add 2 “pin headers” of how many pins each side should have. You can use the search bar in that dialog to make it easier. E.g. a connector with 13 pins in a row would appear if you type 1x13 into the search.
This should give you the connectors. Next is drawing the connections between them. Your boyfreind will likely have to find out what pin connects to what other pin for this part.
You can draw those connections by using the green line button on the right toolbar. The lines can cross in this schematic.
With that part done. Along the top toolbar you will find a button called “annotate” open him and run it. This will name those 2 connectors so kicad knows which is which later on.
Next up is the netlist. Again there is a button along the top called “generate netlist” run him and it saves a file with all those connections.
Next is a button up the top called “cvpcb” here is where you assign the actual footprint / type of connector you will use on the pcb. In your case its just a pin header of x many pins.
And finally we are on to the pcb. Up the top of the schematic editor is a button to open “pcbnew”
With this opener. Up the top is a “netlist” button. Running him should drag in the 2 pin headers you selected and draw white lines showing how you wanted them to connect.
Use the “m” key while hovering over one to move it. And “r” to rotate it. Find out how they need to be spaced and move them accordingly.
Now is joining it all up. On the right hand toolbar is a squiggly green line button he draws the dark lines on the pcb. Run the easy ones first. You also have the other side of the pcb you can route on if things get harder. That the the F.cu and B.cu layers on the right hand side.
And if things get harder still. While drawing a trace you can press “v” to hop to the other layer.
Once you get this far chime back in and I can help you getting the board ordered.