Lost Apple watch- Not on "find my"

So my apple watch has become lost or stolen. It was linked to my phone via Bluetooth, so was on my "find my" before lost.

When it came up lost I went to check that its last location was at the very least in my house. But the watch is completely gone from my devices. I have the serial number info. Is there a way I can add the device back to my account so I can at least see the last location?