Apple id

iCloud uses Apple ID credentials.

If you do not remember the Apple ID Password then follow the steps given in this Apple Article -> If you forgot your Apple ID password - Apple Support

If you do not remember the Apple ID then follow the steps given in this Apple Article -> If you forgot your Apple ID - Apple Support

Once you logged in with another Apple ID then the apps that were purchased through the previous apps may not be available to you with the new Apple ID.

Resolve the issue with the first Apple ID as SravanKrA described, or delete and redownload the applications you're trying to update; it's stored inside them.

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