I don’t have the Apple ID and passcode that were used to set it up how do I pair it with a new iPhone

I don’t have (1) the Apple ID and (2) passcode

1.

See -> Set up your Apple Watch – Apple Support (UK)

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If asked, enter your Apple ID password. If you aren't asked, you can sign in later from the Apple Watch app: tap General > Apple ID, then sign in. 

2.

Read again -> Related Article -> If you can't pair an Apple Watch with your iPhone

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Reset Apple Watch if you don’t know its passcode

If you can't unpair or erase the Apple Watch because you’ve forgotten its passcode, you can reset the watch.

When you reset an Apple Watch instead of unpairing it, the watch is still protected by Activation Lock. Before you can pair the Apple Watch again, you'll have to enter the Apple ID and password that was used to set it up.

1. Put the Apple Watch on its charger.
2. Press and hold the side button until you see Power Off.
3. Press and hold the Digital Crown, then tap Reset.
4. After the Apple Watch unpairs completely, you can pair again. Remember that you'll need the Apple ID and password that were used to set up the watch.