Entity-Relationship Diagram for RT4.4.0

Just wondering if anybody has a better Entity-Relationship Diagram for RT 4.4.0

The problem I have.
I am a consultant Microsoft DBA and work for an organisation that run everything in Microsoft.
Somehow several years back somebody went rogue and decided to purchase RT from a company that is currently charging £100 per month for hosting it and completely fail to provide any support.
The system is no longer being used for new calls but they need access purely for auditing purposes and therefore it only needs to be an archive.
I have managed to backup all the tables from MySQL and have also managed to restore this to MS-SQL Server as flat tables.
Have already managed to extract a list of all the tickets that need to be referenced but struggling a bit to work out the relationship between tickets and especially how to link the History in the tables so I can easily build a report that shows all the details, history and attachments of a ticket (similar to what RT does this but without any options to update)

Another option I have considered is perhaps using PowerBi directly to query MySQL and building a similar report but again I would need to Diagram to help me understand how to put this together.