Unless IBM provides a library for you to do this then you're going to be stuck doing all the TCP/IP calls yourself. It is a custom interface. Having said that a quick google for TN3270 C#
reveals someone wrote a library years ago and posted it on GitHub that supposedly allows you to work with this connection in VB or C#.
I have no knowledge of this library but given their code you can probably figure it out. They also provide sample projects for working with the library so you should start there. You'll need to translate the C# code to VB though. My recommendation is that you compile the library as a C# project and then just reference it in your VB project directly. If you have a private NuGet repo then you could also build it standalone and upload a NuGet package so you can just pull in the dependency like you do everything else.