I'm former FileMaker employee, worked at FileMaker about 6 years, go , so I know almost every bit of FileMaker.
I'am expert at FileMaker products, capable of solving difficult or complicated issues.
You can check my previous finished projects.
Let's discuss in more details.
This is not a simple FileMaker file, but a custom app created using FileMaker, so there's no easy converting.
Since the original developer didn't provide export function, so it's almost impossible to get the data in normal ways.
I'll try to extract the data from the data engine level, and to be honest, no guarantee.