How to Change COM port for FT-8

Can you be a bit more vague?

In SmartCAT you need to be using a TCP Serial CAT port, and in WSJT-X define using that port. Here are some screen shots that will show you what to look for:

Open SmartCAT and create a new port for your WSJT-X operation.  Use the ADD button and select a TCP Port.  Give it a number that is unused, such as 5005, etc.  Select the button that auto-switches it to the slice you are using for FT8, if you wish to use that feature.  Then hit SAVE.

In WSJT setup, as the picture above shows, select "Flexradio 6xxx" in the "Rig" pulldown.
Enter the port number.... 127.0.0.1:5005  (Or whatever port number you have set up.

In the PTT section of the setup screen, select CAT.  This will send your PTT signals via the TCP Port you just defined in the previous steps.  There is no need to select a different port number for PTT.

Select "Data/pkt" in the section that asks for the mode definition.
You may also want to hit the "Fake it" button if that matches your operating style.

Hit "Test CAT" and you should get a green light.  if not, then you haven't set up your TCP port correctly.

Hit "Test PTT" and the rig should switch into transmit mode.   (You may need to hit it again to cancel PTT)

If not, then it isn't registering your CAT port correctly.

Set up a Mic Profile for WSJT that uses DAX TX Audio for input, Low cut and high cut at 0 and 3000 Hz.
Make sure the DAX button is active.

Let me know if this helps.

Ken - NM9P