I don't want to delete the whole configuration (this was the solution in Syncronization - OneDrive) but only to alter and/or review my OneDrive-Sync-Settings. How can I accomplish this?
You won't be able to see your email adress you have used to login for the reason I explained here:
I think there is no option for changing your onedrive Account or to log out at the moment in the GUI. As workaround you probablly could log out of onedrive by deleting the value of sync.3.context in the settings table in the database but be aware that users actually are encouraged to not manipulate the database on their own as this can lead to serious problems such as data loss. Also I haven't tested it and don't take any responsibilty. So you should be careful if you do this.
Additionaly, if I start Joplin at work, it seems that Joplin automagically uses my microsoft business account - instead, I wanted to specify my private account to access my private OneDrive from there
The reason that joplin automatically uses your Business account is that you most likely have ticked the "always login" checkbox in your default Browser for your Business Account. So you should open onedrive in the Browser and log out of your Business Account. When you then click on synchronize the first time after chosen onedrive as sync target you will see the login Dialog in your Browser and you can log in with your private Account. Once logged in with your Private Account in joplin you can again tick the "always login" checkbox for your Business Account if you want.