I lost my Iphone and forgotten my iWatch pass code, what can I do to unlock my iwatch?

Start here;

reset your passcode

And

On a computer, go to iCloud.com and sign in with your Apple ID.

Go to Find Iphone.

Select All Devices, then click your Apple Watch.

Click Erase Apple Watch.

Select Next until the device is erased.

Click the remove button next to your Apple Watch.