Hi there, this is Marc. Thanks for reaching out to the community.
On the Dell, connect it to the internet at the sign-in screen. Bottom-right corner, use the Wi-Fi or Ethernet icon to get it online. Once online, click Sign-in options and choose Password instead of PIN. Enter your Microsoft account password.
If you don’t remember the password, go to another device and reset it at https://account.live.com/password/reset. Once reset, retry logging in on the Dell.
If the laptop still refuses the account and you don’t care about the files, you’ll need to boot from Windows installation media and perform a clean install, creating a new account.
Best regards,