I want to login to Power BI service using other id( say generic service account) , and I am trying to use Incognito mode for the same. But still, in Incognito mode, it signs my id automtically.
Is there any other
Please try different browser, eg: Edge then run it with Inprivate mode, access Power BI service (app.powerbi.com), sign in with your new account.
If it still keep using original account, please clear browser cache then test again. You can also restart the machine if it's convenient.