The support for the MCP2221 in Blinka utilizes the hidapi library. This in turn relies on a few other things which vary for different OS's. So before we can actually use the MCP2221, we need to get everything setup. See the OS specific sections for what we went through to get things working for each.
Just for reference, here's the README from the hidapi source code repo, which has some install information:
But first try the install instructions on the pages that follow for your OS.