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