There are a several of ways to find the correct COM port for the dropController. All use a similar method but wear different clothes. Here are an easy two.
1. Use the dropController Windows App
2. Use Windows device manager
Once Windows has assigned a COM port it seldom moves so you should only need to do this once.
Use the dropController Windows App
In my case I have COM7 only. Since the dropController is not connected I know COM7 is not the dropController.
Now connect the dropController to the computer and wait for the beep bop burb.
To confirm try connecting.
Because you connected the dropController after starting the app, the app may fail to connect on the first try. If this happens just try again.
Use Windows device manager
If you have one open expand it and note the COM ports listed.
CH340 is the USB to serial adapter chip on the Arduino Nanos I provide. If you are using your own Arduino then the entry may say CH340 or FTDI.