Reset email address without password

I registered using my facebook account many years ago. In the meantime I changed my email address on facebook and I can no longer access the old address. My old address still appears on Musescore, but to change it, it asks me for a password that I have never set. How do I figure out which password to use? How do I change my email address and create a specific account on Musescore? (Without losing my profile)