Hello Scott, the zapper isn't happy in Win10, or perhaps I should say Win10 doesn't like it, so use the File Explorer (Windows key + E) and navigate to the folder where you want to zap the .BDP files. A search for *.BDP will find them all in moments and you can delete 'em from the search results.
You can be selective and just delete from the Aircraft directory, or Buildings, or whatever suits, but by default all sub-folders are included in the search, so if you search for and delete from the main ETO directory f'rinstance, all .BDP files will be deleted. This means the sim has to rebuild the whole lot next time it boots and you'll be making a cuppa while waiting. Use carefully!
If I'm modding something I try to be quite selective and only zap what needs to be.