How to wipe Apple Watch

I have an Apple Watch series 2 I’m trying to sell. I need to completely erase and factory reset the device but I have a few problems:

1. screen is broken and unresponsive though Apple Watch still works
2. no longer have phone that was paired to it
3. Watch is not connected to internet

any ideas for how I could still erase it? I tried erasing it through ICloud and it says it will do so when it connects to the internet. Is this problem solved or is there more that needs to be done?

Thanks in advance!