How to do filtering using LINQ?

I'm trying to replicate the sample from "Using Linq as data source" provided in the demos. I was able to successfully set up a lookup in the config sheet, however, I could not make the filtering work as I wanted. The documentation specifies that to use "Filtering Data" with LINQ, I should use the built-in parser syntax. Any tips on how I can accomplish this?

var report = new FlexCelReport(true);
report.SetValue("Date", DateTime.Now);

report.AddTable("Data", data);
report.AddTable("Employees", employees);
report.AddTable("Companies", companies);

report.AddRelationship("Employees", "Data", "Id", "VerifiedBy");
report.AddRelationship("Companies", "Data", "Id", "Company");
report.AddRelationship("Employees", "Companies", "Company", "Id");

report.Run($"D:\\reports\\TemplateReport.xlsx", "D:\\reports\\report.xlsx");