Hi Sheereen, if you have elasticsearch data located in the .data folder already, then you should be able to view that using elasticsearch API request from the Console app (dev tools) in kibana's main application.
If you then want to build on top of that data, which it seems like you do, then you can use the elasticsearch service from the context in your plugin's setup and start contracts.
The docs for the Core APIs cover how to use them: Kibana Core API | Kibana Guide [8.5] | Elastic and the suggested patterns to follow are discussed in these docs.
To use services from another kibana plugins (like dataviews for example), there's a great post that explains what approach to take and some examples you can look at here