forgot apple id

inaam179 wrote:

That's what i am trying to ask that how do i remove activation lock when my father don't remember the apple ID?

You don't.

If he doesn't remember his ID, he will have to recover the ID (start here: https://iforgot.apple.com) or he will have to provide Apple with the original proof of purchase for the watch to have the activation lock removed.

Then you have to remove the activation lock.

About Activation Lock on your Apple Watch - Apple Support

What to do before you sell, give away or trade in your Apple Watch, or buy one from someone else – Apple Support

See here;

If you've forgotten your Apple ID – Apple Support

The ID on the watch is the same as the ID on the phone is is paired with.

It has to be. Otherwise, it would not have worked with the phone.