Ken,
You can manually change the com port assignment in Windows.
Basically, you use the following steps:
1) Go into your Device Manager
2) Go to Ports (COM & LPT)
3) Look for the Microbit port you wish to change
4) Right click and go to Properties
5) Go to "Port Settings"
6) Click on "Advanced"
7) Change the port number below as required
Save and you should be ok.
Caveat: I noticed that for some reason the Port Settings tab is missing from my
installation. I assume that this is a bug, and may or not be available in other Windows
installations. These directions are generic for all COM devices in Windows.
73,
Mitch DJ0QN / K7DX