Hi! I also wanted to know the answer to this question. I don't know what I'm doing, so this is likely not the best way, but here's at least a work-around I got to work: Instead of looking at and trying to modify the training samples from the training samples manager, add them to the map as a shapefile, i.e. Add Data (not within Training Samples Manager). Then one can select the offending polygons on the map in the ways you're probably used to (what's usual for polygons that aren't training samples), and delete. I was worried that the shapefile might not open back up in the training samples manager properly after I did this with my issue, but it did (after I saved everything, closed the map, re-opened it, and removed the shapefile from the map). Appears as before, less the polygons I removed.
