How do I get a new passcode for the iPhone this attached to this iCloud account?

Passcode to open the phone is not directly connected to the icloud account

If you forgot the passcode on your iPhone, or your iPhone is disabled

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How to re your iPhone if you forgot your passcode - Apple Support

You need a computer and it will wipe the phone

If you had attempted unlocking multiple times with incorrect Lock Screen passcode, or if a message says that your device is disabled, learn what you need, what you get and what is lost.

You need a computer to follow these steps. If you don't have a computer, borrow one from a friend.

Forgot? Click below to reset…

Click->If you forgot the passcode for your iPhone, iPad, or iPod touch, or your ...

Regarding your data, If…

1. You have an iCloud or iTunes latest backup, then there is nothing to worry. If not read more...
2. You have synced your data to iCloud, then what you will get back is what you have synced to iCloud and uploaded to iCloud Drive; like the information that are synced and stored in iCloud are, Contacts, Calendars, Bookmarks, Mail, Notes, Voice Memos, shared photos, iCloud Photos*, Health data, call history, and files you store in iCloud Drive. (*-If you had turned on iCloud Photos, your content is automatically stored in iCloud.)
3. You have not backed up or do not have latest backup, nor imported nor you have synced nor uploaded your data to cloud drives prior to the situation that you are in, then I am sorry, all your data is lost.