Apple Watch locked when restarting after long powered-down state
To troubleshoot, I would follow the restore steps:

https://support.apple.com/en-us/HT204505

It mentions that bluetooth should be on on the phone and you should be connected to WiFi so if you can turn both of those on on both devices (might be hard on watch unless it prompts you) but if you can get the same WiFi router as the last time it booted, it might reconnect automatically.
Once that’s done, you might end up down the “watch won’t restart” article which has a few more things to try before you contact Apple Support. Even though force restarting the watch isn’t ideal, you might try that as well one time once WiFi and Bluetooth are enabled to the max extent you can manage.

force restart - https://support.apple.com/en-us/HT204510
reset and restore - https://support.apple.com/en-us/HT204567