How do I track my Apple Watch if it is offline?

According to Apple:

If you didn't turn on Find My before your Apple Watch was lost or stolen and your watch isn't connected to Wi-Fi, cellular, or your paired iPhone, you can't use it to locate your device.

◁Apple Watch User Guide▷

See this link and follow the instructions provided

If your Apple Watch is lost or stolen - Apple Support

If it's offline then you can only try and find it by looking manually for it.