I am not able to update WhatsApp with new Apple ID

Why did you create a new Apple ID? You lost your phone, not your Apple ID. You should never create a new Apple ID unless absolutely necessary. Losing the iPhone does not require you to create a new Apple ID.

Sign in with your old Apple ID since all your Apps are tied to it.

Or delete the WhatsApp App, and download it with the new Apple ID.

Hello Sandhya,

There was no need to create a new Apple ID. An ID isn't part of a particular device, it is part of everything you do with Apple. Anything you bought with the old ID is tied to that ID. You will now have to either re-purchase your things with the new ID or still use the old ID to Family Share with the new ID. In that case you might as well use the old ID. Change your password on the old ID if you have not done so already.

Please read this link -->

Change your Apple ID password - You may also wish to turn off "Find My" before changing information and turn it on again afterward. - https://support.apple.com/HT201355

"After you change your Apple ID email address or password, you might need to update your sign-in information with any Apple services you're using" Click on this link to read "What to do after [or before] you change your Apple ID email address or password" --> https://support.apple.com/HT204071

- This is particularly important to do if you use the "Find My" feature. Disable Find My before changing your information, change the information, then reactivate it with the new information.

To turn Find My on and off:

For devices with iOS12 and earlier, or Macs with Mojave or earlier read this link on how to Set up Find My iPhone on all of your devices" - https://support.apple.com/HT205362

Home screen > Settings > [your Apple ID] > iCloud > Find My > turn on/off

For devices with iOS 13 or later, or Macs with Catalina or later read this on how to "Set up Find My on your iPhone, Mac, AirPods, or other devices" - https://support.apple.com/HT210400

[mobile devices:] How to turn on/off Find My for your iPhone, iPad, or iPod touch

Home screen > Settings> Name > Find My > on/off