To understand the existing table structure of an unknown Power Platform environment I use tools like the XRM Tool Box. The plugin ‘ERD Schema Generator‘ allows you to generate an Entity Relational Diagram.
Quick steps
- Optional download and install XRM Tool box
- Start the XRM tool box
- Create a connection to the (Power Platform) environment
- Install / find and activate the “ERD Schema Generator” plugin from the tools menu
- Load all entities (from a solution)
- Generate the diagram with help from the diagram.io website

After starting XRM Tool box, create a connection to the Power Platform environment.
Then find the ERD Schema generator from the Tools menu.

Example, the generated ERD Diagram

See also: dbdiagram.io