where can i access phpmyadmin from plesk?

I'm not sure since I'm not using it but I believe it is using an older version if it is using one. Recently a new version of the software came out and you can download it from sourceforge.net. If you've installed/developed any scripts before it is a breeze.

Remembter to secure the directory you have phpMyadmin installed in if you go that route.

Select your domain; Click the Databases button; Click on the name of your database; Click on the PHPMYADMIN button on the right hand side...

You'll be able to access just the specific database you've selected. If you need additional functionality, you can install phpMyAdmin on your server manually.