I can not update Whatsapp

There's a difference between Apple IDs and Apple ID accounts. An Apple ID is basically an email address and you can change your email address on a single account. However, if you set up multiple accounts you are actually using different accounts each with its own Apple ID. Items purchased with one account cannot be updated on a device signed in under a different account. You have to re-download the app under that account after having first deleting the app set up under the old account (doing so may result in loss of settings).

So it depends upon what you actually changed.

(Yeah, yeah, Apple needs to improve its naming things such as producing 2 iPhone models in the space of a few years with identical identifiers which in turn were also identical to a computer model that was made many years ago -- don't get me onto my soapbox :-) ).