I’m trying to repair my Apple Watch to my iPhone but I can’t remember my Apple ID that I originally paired my watch with

Request an Online Activation Lock Removal 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 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.

Otherwise the watch will be of no use to you.