How to remove a activation lock on an Apple Watch if I don’t remember the iCloud that was an old iCloud I have a new one anI want to use my Apple Watch

You will need to know the Apple ID and passcode in order to remove it. You can start the ID recovery process here:

If you forgot your Apple ID - Apple Support

If you have the original receipt, you can also contact Apple and see if they will remove the activation lock with that documentation.

Checkout the following article for how to remove activation lock. https://support.apple.com/en-gb/HT201441

I forgot my old iCloud on my Apple Watch and I wan to use the Apple Watch

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.

Read the posts above yours.