Let me discuss a few things and help you get your desktop app installed.
QuickBooks Online (QBO) doesn't require any password to get its desktop app installed. But your computer or laptop might be asking you to enter your admin login credentials when installing new software, like the QBO desktop app.
If you're prompted with a different popup other than the admin login, I recommend closing it and deleting the QBO desktop app install setup file. Then, please try redownloading the setup file here: https://quickbooks.intuit.com/apps.
If you get the same result, I suggest contacting ourQuickBooks Customer Care. They have extra tools, like screen sharing, to help check the root cause of the issue and get it fixed.
Please let us know if you have any other questions. We're always here to help.