Unfortunately Certbot’s standard setup instructions don’t work well with Bitnami, and Bitnami’s own tutorials are somewhat lacking too. There’s a (long) recent thread about it here. I’d suggest reading it as there are quite a few things that can go wrong!
The most immediate answer though is that your guess about the location of your webroot was probably wrong. Since you’re using wordpress, I’ll hazard a guess that it’s in the same place as in that other thread: /opt/bitnami/apps/wordpress/htdocs