How do I create a new icloud email address on my ipad so I can change my apple id email address?

If your primary email address is already an Apple email address - and not the address of a third-party email account - then then the primary email address cannot be changed. You can create up to three additional alias addresses, however, it is my understanding that you cannot change the primary address from that that already exists.

This support page may provide useful additional information:

Use email aliases on iCloud.com - Apple Support

If you need to update your primary email address, this being used to identify and sign-in to your AppleID account, you simply need to update your existing account information:

Change your Apple ID - Apple Support

What to do after you change your Apple ID or password - Apple Support

Creating and using an entirely new AppleID is neither necessary nor advised.

Consider that all you purchased Apps, Subscriptions and Apple Services are permanently associated with the AppleID account from which the purchase was made. Using a different AppleID will lose access to all existing purchases. These purchases cannot be transferred to a new AppleID.