Hey, the easiest way to open a BSM file is to double-click on it and let your PC decide which default application should open the file. If no program opens the BSM file then you probably don't have an application installed that can view and/or edit BSM files.
Warning: Take great care when opening executable file formats received via email or downloaded from websites you're not familiar with. See my List of Executable File Extensions for a listing of file extensions to avoid and why.
As of this writing, I don't have information on any specific applications that will view BSM files or open BSM files for editing. If you know of any, please send me a quick email and let me know the name of the program so I can update this page.
Tip: Use Notepad or another text editor to open the BSM file. Many files are text-only files meaning no matter the file extension, a text editor may be able to properly display the file's contents. This may or may not be the case with BSM files but it's worth a try.
If you find that an application on your PC does try to open the BSM file but it's the wrong application or if you would rather have another installed program open BSM files, see my How to Change the Default Program for a Specific File Extension guide for making that change in Windows.