If I no longer have the iphone my apple watch is connected to, and I didn't disconnect that apple watch from that phone how can I reset the apple watch to pair to my new iphone?

You have to unpair the watch from your old phone here;

From a web browser,sign in to iCloud.com with your Apple ID.

Go to Find iPhone.

Click All Devices at the top of the screen.

Click your Apple Watch.

Click Erase [device]. Select Next until the device is erased.

Click Remove from Account.

Then go here;

How to pair your Apple Watch with a new iPhone