What is the cost for doing this, out of curiosity? If OP only earns a trickle of revenue from their site, it probably isn’t even worth the money (?)
A lot of lawyers will give a free consultation, and in my experience (not for IP) they will give decent expert advice for free. No harm calling them.
He earns 7 figs a month from it iirc, was featured many times on HN as a successful indie hacker.
Most state bar associations have a free consultation line that will refer you to a reputable lawyer to start with and do basic consultation on where your issue should go and how much it will be. If I had to guess, getting advice is probably $100 and having a lawyer send a letter is $250-500.