There is no precise drop-in replacement device for the old TOPSwitch-FX series. A TOPSwitch-JX is recommended as replacement. Exact configuration would depend on how you used the TOP-FX "M" pin in your previous application. Unfortunately, the FX and JX series are not pin-compatible.
The best approach for device selection would be to either download the PI-Expert suite or use the online version, and load the input and output parameters for your previous design into the TOP-JX PIXLS spreadsheet, as well as the turns, core data and primary inductance of the transformer you're currently using. The spreadsheet will automatically select an appropriate JX device based on power supply and transformer parameters, as well as giving you suggested values for surrounding components. You can force the transformer parameters by entering them manually rather than allowing the spreadsheet to automatically select them. You should be able to re-use the old transformer in the new design, as long as the output power and operating frequency remain the same. You may need to trim the device current limit using the TOP-JX "X" pin in order to assure compatibility with your current transformer design. You also have the option of selecting a larger device and trimming down the current limit via the "X" pin for lower conduction loss.