How to wipe my Apple Watch data when I don’t have access to Find My?

I lost my Apple Watch about 7 days ago and I don’t have find my on. I am so stupid not to have done that when I got it. So I know I have no hope finding it but it is mirror to my phone. How do I delete important stuff?

[Re-Titled by Moderator]

Original Title: I lost my Apple Watch 7 days ago