Sorry to say there is no way. MSB files don't contain mxml files so there's no ground for an abc export.
There are (mainly) either PDF files or chordpro files that are in use in MSP (and I'm not sure if they can be easily extracted from msb which is only an export format for MS).
There's mxml and abc support planned for the future (and I'm one eagerly looking forward to ABC support), but the info for such an export has to be already in the files which isn't in the files generally used in MS.
If you have files from notation software like Musescore, Finale, Sibelius etc. you can export these to MXML and then convert to ABC.
I very much always recommend the webpages of Jef and Wim regarding ABC and MXML
http://moinejf.free.fr
http://moinejf.free.fr/js/edit-1.xhtml
https://wim.vree.org/svgParse/index.html
https://wim.vree.org/js/xml2abc-js.html
There are (mainly) either PDF files or chordpro files that are in use in MSP (and I'm not sure if they can be easily extracted from msb which is only an export format for MS).
There's mxml and abc support planned for the future (and I'm one eagerly looking forward to ABC support), but the info for such an export has to be already in the files which isn't in the files generally used in MS.
If you have files from notation software like Musescore, Finale, Sibelius etc. you can export these to MXML and then convert to ABC.
I very much always recommend the webpages of Jef and Wim regarding ABC and MXML
http://moinejf.free.fr
http://moinejf.free.fr/js/edit-1.xhtml
https://wim.vree.org/svgParse/index.html
https://wim.vree.org/js/xml2abc-js.html