When I was working with Windows machines among a group of other software developers and testers, we sometimes needed to get into a computer after its original user had left the company. It was easy to find tools on the Internet that would do that. One, I remember, simply set a password to blank, after which the new user of that machine could set their own.
The last time I needed that tool was many years ago, and I don't recall the name right now, but we found it easily with a little web search. I'll bet you could do the same.