Removing Apple Watch from account with Stolen Device Protection

I removed my old watch from my phone, but did erase the data yet. Now my old watch still keeps my data but I can’t remove or unpair it because it doesn’t show up in my phone anymore. Nor can I remove it from my account through iCloud due to Stolen Device Protection is turned on. What can I do to completely erase the watch?

[Re-Titled by Moderator]