I have an older Coleman generator (5 KW) that a 240 Volt duplex outlet 20 AMP. I have a transfer switch rated for 5 KW that has a twist lock connector. How do I make a cord to go from my generator to the transfer switch without having to re-wire my generator?

Thanks,

Stan

You DO NOT.
Your genny has a 3-wire straight 240v receptacle. Your transfer switch requires a 120/240v 4-wire receptacle.