icloud apple id has old id

If you want to change your iCloud ID to another existing ID you'll have to delete the account, create a new account with the other ID, and migrate your data to the new account. To do this, first go to Settings>iCloud on your phone and turn all data you are syncing with iCloud (contacts, calendars, etc.) to Off. When prompted choose to keep the data on your iPhone. After everything is turned off, scroll to the bottom and tap Delete Account. Next, set up a new iCloud account using your other ID, then turn syncing for your data (contacts, etc.) back to On. When prompted, choose Merge. This will upload the data to your new account.

Go to System Preferences on macbook - select Internet Accounts - left side will show all your current accounts -right click on account and delete those accounts using wrong email address/id - then go back out and add the right accounts - this fixed my iCloud popup with old email/apple id

I had this same issue (my OLD apple ID was showing under iCloud - grayed out/unable to edit, but my NEW one showed everywhere else.)

I had to sign off iCloud from my iPhone (Settings, iCloud, Sign Out), then sign back in with my new apple ID. *note: it prompted me to delete all photos, etc when signing out, which made me nervous - but these returned after I signed back in with my new apple ID and merged with the cloud (following the prompt from the Camera setting).

I hope this helps someone else who was frustrated after following all the other answers with no luck!