OK, I do not claim to be an Arduino expert or troubleshooter by any means.
However I can offer these observations that may help-
Try booting the Arduino software without the FT-5 board connected (no USB cable).
On the top menu bar select Tools, then Ports.
It should list a port or two depending upon what your computer is equipped with.
Now power up the Arduino board (the printer) and connect the USB cable.
Caution, do NOT ever power down the printer without first disconnecting the USB cable.
Hopefully after a few seconds another port will appear (on mine it happens to be COM4).
This is the one to select.
Now under the Tools menu item again, select Board, then select "Arduino/Genuino Mega or Mega 2560".
Next, under the Tools menu again, select Processor and then select "Atmega 2560".
You should now be ready to upload a "sketch" (the odd name they use for a compiled program).
If you do not see a new COM port appear when connecting the USB with the board powered up, that indicates that the USB hardware is not being recognized.
Most likely that means that you did not install the hardware driver for it (or that the install failed).
The driver is part of the Arduino package as I recall.
You may need to do the installation again.
I hope this helps.