Modification to API client library, written in C# exposed to COM

Currently we have a COM Exposed class library so the customer can use in vb6, the library is written in C# .NET 3.5 and uses JSON and SharpCompress. However modifications are needed to this library as some of it is not working correctly. Additionally the customer is asking some questions i cannot get my head around. If your work is good on this project it will lead to future projects as im recruiting developers for this project. Ideally the candidate would have knowledge of vb6 and be fluent in C# .NET v 3.5