My Apple Watch SE (1st generation) won’t connect to my iPhone 15 pro max

I recently bought a new iPhone 15 pro max recently and my Apple Watch SE (1st generation) won’t pair to it. I’ve tried unpairing it from my old phone and it still won’t pair to my iPhone 15 pro max - it won’t even pair with my old phone I unpaired it from. I’ve also tried resetting network settings - that didn’t work. I’ve tried force restarting it. And I’ve tried follow instructions from YouTube videos - which is what said to reset network settings. Does anyone know what I can do to fix it?