i can't connect my watch of my new iphone 11pro and i forgot my old apple id i used to my watch series 4

See the Apple Support article(s) below.

Watch isn't connected or paired with your iPhone

Watch - pair with a new iPhone

See if you can recover the ID/password. Use every email address you can think of.

Apple ID - How to find your Apple    An iCloud e-mail address is an Apple ID.

Apple ID - Find              

For the Apple ID password, enter the Apple (iCloud) ID and click Forgot Password. See if you can get an email option if necessary.

Apple ID - Manage            

Apple ID – Forgot Password