My Apple ID is setup correctly on my phone , but when I try to setup my watch an old email keeps popping up as my Apple ID … how to delete the old email and Apple ID

You can ask apple to remove the activation lock online on this page;

Remove the Activation Lock Here.

Or this;

If you can't remember/gain access to the apple id that paired the watch to the phone.Take the watch and it's receipt with the serial number along with some photo id and any other proof of ownership to an Apple Store and request that they remove the Activation Lock for you.