When I started using a password manager I did this: change repeating passwords, and delete info on sites I don't use any more. JustDeleteMe [0] has a good list of account deletion methods and links for different pages.

[0] https://justdeleteme.xyz/index.html

Not all sites offer that, especially smaller ones. I've had to deal with this before, and even emailing every contact email I could find doesn't help. I ended up changing the passphrases of all the other services instead.

Sadly that's either obscure or unavailable for majority of sites.

(similarly and a major peeve - vast majority of signup verification emails do not have a "no this is NOT me that signed up, delete this email" option! My email gets misused a lot in some countries where my name is common and I have no easy recourse to deny it)