Where do I find the newly required 4-digit passcode to open my iphone?

Hi Eric - Thank you for your help but I think I misstated my question. I get a message to "Update Apple ID settings. Some account services will not be available until you sign in again. Then it says to "Confirm your iPhone passcode to keep using iCloud. This passcode also protects access to data stored in iCloud. "

This is where it requires me put in a 4-digit passcode that I've never created. So I've given my user name and password for Apple ID, then I put in my 6-digit passcode that I use to open my phone, and THEN it asks for the mysterious 4-digit passcode. I am not able to get iCloud on my iMac or my phone until I figure this out. Does your previous answer still hold? I need to reset my phone? Thanks. Sorry if I'm not getting this.