How do I fix iPhone XR asking for a 6-digit password when I never set?

I transfer from my old iPhone 7 to an iPhone XR. It was working well on day 1 but on day two, it asked me for a 6 digit password and not 4 like on my old iPhone 7. I never set up a 6 digit password on iPhone XR. My phone is now blocked and I’m unsure what to do. Eg. My old phone’s password was 1234. If I put 1234 on my XR device, it doesn’t work as 6 digits are needed but I didn’t set one up. I’ve put a cable onto my computer to restore my phone but it fails and it tells me the software on my device was corrupted. Please advise! Thank you

[Re-Titled by Moderator]

Original Title: Password migrating from 4 digits to 6 digits