JOSM is a widely used desktop application for editing map information for the openstreetmap.org project. This project aims – with the thorough help of the community – to create open source, accurate and extensive map information of the whole world and for different purposes.
To commit to this project, one thing you can do is to use your recorded GPS data from your Garmin device (so called .TCX files) and validate the OSM map against it. Advanced users might run JOSM for achieving this. Former versions of JOSM provided a special plugin, called „tcximport“er. Latest JOSM versions simply inform the user at startup that this plugin is no longer used…
However, there is no function in JOSM out of the box to still import the TCX files. The glue is: you still need to install a plugin, but it has a different name and functionality.
Simply open the settings dialog and search for „import“. You will get a list of relevant plugins, including the „dataimport“ plugin. Installing this, extends the file filter in the „open file“ dialogue, including .tcx files.
Unfortunately this is hardly documented, at least it works, so keep on logging and mapping!