How do I pair my watch to my new IPhone if I don’t remember my Apple ID or password used at the time I set it up?

You are going to have to either recover your Apple ID, which you should only have one and you need to use it on your iPhone, so you should be able to see it there, then you only need to recover your password if you cannot remember that. If you forgot your Apple ID password - Apple Support Otherwise, you will need to request Apple unlock the Activation Lock. You can request that online, however you will need a copy of your original receipt for the Watch with the watch description and serial number. How to remove Activation Lock - Apple Support

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

Online Activation Lock Removal Tool.

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 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.

If you activated the new phone, then you should know the Apple ID you used. Also, it should be the same Apple ID you used before, and the same one you used to activate your Apple Watch. You should only have one Apple ID.

I need my Apple ID for my new iPhone to pair my watch