Can't change my email

My current email is one that I don't recognise and seems auto-generated, which means I don't have access to it and can't log in other places like the box-app on my Mac or my phone. The reason I got into my account in the first place was that it automatically signed me in with that (seemingly autogenerated) email. When I try to link an email to my account, an error message appears saying "There was an error while trying to add 'new email adress' to your account". How do I fix this? Thank you for help.