In the Help menu select “check for Updates” and click on “Download CTY.DAT” if it shows the availability of a new version. If the “Update CTY.DAT automatically” box is checked in that window, DX Monitor will automatically download the latest CTY.DAT file directly from the country files web site. After the new CTY.DAT file is downloaded, it will be necessary to restart DX Monitor.
DX Monitor checks the file header of https://www.country-files.com/