That wouldnât be necessary. Youâd just have to sign out of iCloud, then sign in with the old ID.
Be aware that the backups of the ID youâre using now will not be available any more. The current iCloud email address will be removed from your device, together with your emails, notes, calendar events and contacts. Depending on your settings, that might also affect photos, Safari bookmarks, messages, âŚ
If memory serves right, itâs possible to keep apps purchased with the new ID and data connected to it on the iPhone, at some point.
If you really want to start over with your old iCloud/Apple ID, go to Settings - your name - iCloud, turn off Find My iPhone, then sign out of iCloud. That done, go to Settings - General - Reset - Erase All Content And Settings. That will set back your device to factory settings.
That done, set up your iPhone with the old ID. After setting up Wi-Fi, make sure you either use âRestore from iCloud Backupâ (if itâs still available from your previous ID), or âDonât Transfer Apps & Dataâ. Sign in with your old iCloud ID and password.
Set up your iPhone, iPad, or iPod touch