Reset Windows 10 Professional Password while I cannot boot

I have kind of chicken-and-egg delimma. Yesterday, all of a sudden, my Dell XPS 15 did not boot properly, and showed the error "The digital signature for this file could not be verified for this file. Error code: 0xc0000428". What magnifies my problem is I forgot my admin password (only account on this machine) as I have been using fingerprint for more than 2 years now. However, I cannot reach the figerprint screen anymore with this boot error. Here is what I tried:

1. Used Boot USB to start repair. It redirects me to choose account, then I am blocked because I do not remember the password
2. Change my MS password online (it is "outlook" account). It still does not accept the new password. I am wondering if it is because I do not reach the sign-in screen, it only checks against the last used local password!
3. Tried the ulitman trick. It did not work, and it will not help because I can't reach the login screen to utilize the utility manager to change the password
4. To fix the error of "The digital signature ..." I tried to disable that from Startup options. When I click "restart" it does not take me to startup options where I can disable the digital signature enforcement (with F7), but it takes me to the original error screen.