It sounds like instead of simply changing the email address used on your one account, you instead effected an email address change by creating a second account. As a result, the request for an old account can happen if there are apps (or media purchases) on the device that were installed (or downloaded) under a different Apple ID, and they need updating or redownloading.
The best thing to do would be to go back to using the old account and change the email address you used for it. However, you won't be able to use the one you just used to create this second account.
Alternatively you can resolve this by deleting the item(s) requesting the update, and then download the apps and games again using the Apple ID that is signed in with the device.
You want to be careful that you do not lose any data, so be sure to check with the app developer to determine if removing the app will cause data loss.
These steps from "Delete apps on your iPhone, iPad, and iPod touch" [at: Delete apps on your iPhone, iPad, and iPod touch - Apple Support ] will help you remove the app:
How to delete an app
1. Touch and hold the app.
2. Tap Remove App [the "-" icon]. Remove App is the third option in the menu.
3. Tap Delete App, then tap Delete to confirm.
Keep in mind that some built-in Apple apps can't be deleted from your device, so you might not see the option to delete an app. Here’s a list of built-in Apple apps you can delete from your device [at: Delete built-in Apple apps from your iPhone, iPad, or Apple Watch - Apple Support ]. If you can't delete an app that's not made by Apple, disable parental controls [see: Use parental controls on your child's iPhone, iPad, and iPod touch - Apple Support ], then try deleting the app again.
If you touch and hold an app from the Home Screen and the apps start to jiggle:
1. Tap the Remove icon in the upper-left corner of the app. (There's also an Add button in the top left corner of the screen and a Done button in the top right corner of the screen.)
2. Tap Delete App, then tap Delete to confirm.
3. Tap Done.
Once deleted, adding the app using the correct Apple ID should resolve the issue. See the article: Download apps and games on your iPhone or iPad [ Download apps and games on your iPhone or iPad - Apple Support ]
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This is modified slightly (for carry-over of linked documents) from a Community Specialist post: how do i get ride of a old id - Apple Community