How to set up existing watch
Trying to set up an existing Apple Watch with new iPhone 14 Pro Max. I don’t know how to make the watch searchable for Bluetooth.
Apple Watch SE, watchOS 9
You may be trying to pair it without unpairing from the old phone. Watch cannot be paired to two phones.
Whether or not you have access to your old phone your options to pair your watch are in this article.
How to pair your Apple Watch with a new iPhone - Apple Support