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
Start the dropController app without connecting the dropController device and jump to the Settings tab
On the Settings tab, click the R button to refresh the COM port list.
Open the COM port drop down list and note what COM ports in the list.
In my case I have COM7 only. Since the dropController is not connected I know COM7 is not the dropController.
Connect the dropController to the computer and wait for the beep bop burb.
Refresh the COM port list again.
Open the COM port drop down list again and you should see an extra entry. In my case it is COM6. This is the dropController.
To confirm try connecting.
Because the dropController was connected after starting the app, the app may fail to connect on the first try. If this happens just try again.
Use Windows device manager
Without connecting the dropController to your computer, open Control Panel and then Device Manager
Look for an entry labelled Ports (COM & LPT).
There may be or not be one. In my case I do not have one.
If you have a Ports (COM & LPT) entry, expand it and note the COM ports listed.
Connect the dropController and after a short pause the Device Manager list will auto update.
I now have a Ports (COM & LPT) entry.
Expand the Ports (COM & LPT) entry, I can see I have an entry named USB-SERIAL CH340 (COM6)
Your COM port is likely to be different. For me, the dropController is on COM6.
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 or something else.