How to convert an existing design from USB Mini/Micro to use USB Type-C connector?
The FT232 is full-speed (12mbps) USB device, so you can't possibly take any advantage of Type-C high-speed connector.

To make your FT232 design with Type-C receptacle, all you need is to wire your D+/D- to PAIR of D+/D- pins on Type-C (to both pairs in parallel) receptacle, and pull down both CC1 and CC2 pins to ground with 5.1k resistors.