Hi, I'm Robinson, and I’m happy to help you today.
I know how frustrating this may be for you but I'll do my very best to help you.
You can use the same account and password that you use to login on Windows if this account has Administrator rights.
Another option to is to use a bootable USB to use command prompt without need a user.
1-Create a USB device with an installation image.
You can create using the media creation tool, download it on this link.
https://www.microsoft.com/en-us/software-downlo...
2-Enter on BIOS/UEFI and change to boot from the USB device.
3-On installation screen click on "Repair your pc" on the left bottom
4-Click on "Troubleshoot" then the Advanced Options page will appear.
5-Click on "Command Prompt".