I can show you how to save it, onlinedepartment.
QuickBooks Online uses your browser's setting to save a password. When you log in, you'll see a pop-up asking if you'd like to save it or not.
The screenshot below is for the Google Chrome. You can also click on the key icon to appear it again.
When you log back in, you'll notice that the User ID and Password are auto-filled.
You can also reset your password or recover your user ID if you've forgotten it.
I'm looking forward to hearing from you again. Have a great day!