new OS is not working for my watch series3. cannot pair my phone. what should i do to fix the problem?

The Apple Watch Series 3 cannot update further then watchOS 8 series.

For pairing problems, see this link and follow the instructions provided

If you can't pair an Apple Watch with your iPhone - Apple Support

If you are having difficulty updating your series 3 watch to WatchOS 8.7.1, make sure your iPhone is updated to iOS 16.1.1. This solved the pairing issues for many.