I forgot my old Apple ID that was connected to my watch

Your old Appel ID could be recovered:

If you forgot your Apple ID - Apple Support

If you forgot your Apple ID password - Apple Support

In any other case, contact Apple Support and show them the purchase receipt of the Apple Watch. Then they might be able to switch off the Activation lock.

Apple Support Phone numbers

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.