how to access data from old icloud account on iPhone 8

What database are you referring to? Do you mean accessing iCloud Drive? If so, it's now called Files and if you don't see it on your phone (on any screen), you could download from the App Store.

You could also go to iCloud.com and see what you have stored in the various apps, e.g. Notes, Reminders, Contacts, Photos, etc.

Have you tried signing in using the old Apple (iCloud) ID? Do you have a backup made with that ID that you can restore from?