Notejoy does not offer a quick account switching mechanism, so if you need to switch between Notejoy accounts you'll need to logout and login again.
A common way people manage this is to use your web browser's incognito window to login to a different Notejoy account. Or alternatively, login to one account with the Notejoy desktop app and login to a different Notejoy account from your web browser.
You should ask yourself though whether you really need multiple accounts. Notejoy's team library mechanism makes it very easy to collaborate with multiple groups of people as each library is independently shared with a team. No one can see the other team libraries that you are part of nor can they see any of your personal notes inside your personal library. Because of this, most of our users use a single Notejoy account for personal and professional use.