Converting .mbz to older version

If this is in an inappropriate section, please move it to an appropriate one.

My problem:

I have created several Moodle lessons on the testservers demo.moodle.net and test.moodle2.de, and made .mbz-backups of them - which are of version 2.3.2.

Unfortunately, I need to restore those .mbz-lessons on a different Moodle server which uses version 2.3.1+. That did not work, the server went into a timeout, and if the restoring did work at all, the lessons could not be opened.

Now, is there any way I could convert those .mbz files to a lower version? Is there a testserver that uses an older Moodle version? I am absolutely clueless and thankful for ANY help.