I am sorry you are having trouble with the Wixel software. I recently tested the Wixel Configuration Utility on macOS 10.13.4 and it seemed to work. What version of macOS are you using on your MacBook?
To make sure you have the latest version of the Wixel software for macOS, please use the download link from the “Installing Mac OS X Drivers and Software” section of the Pololu Wixel User’s Guide.
The name of the file you download should be wixel-mac-151127.dmg. Please check the name of the file after you download it and let me know if it is different from that.
After downloading the file, please double-click it to open it. You should see a few icons, one of which says “Pololu Wixel Configuration Utility”. Please double-click on “Pololu Wixel Configuration Utility”, and post a screenshot if you get an error at that point. The idea of this test is to just keep things as simple as possible and see if you can run the software directly from the .dmg file without installing or copying anything.
Also, please try disconnecting all Wixels from your computer before running the software, and let me know if that changes anything.