Reinstalled Windows and now don't know my Outlook password

if it's an Outlook or Hotmail address, that password is just your Microsoft account password, so use the Forgot password option on the Microsoft sign in page. It sends a code to your recovery phone or email. No access to either of those? Then it's the account recovery form, answer as much as you can remember (old passwords, subjects of recent emails, contacts). Also worth checking if Chrome or your phone saved the password, look in the password manager on any device that's still signed in.