There is no good course of action.

Back in the earlier days of VB.NET, up through VS2008, there was a conversion tool that did a pretty poor job of converting VB6 into VB.NET. Some people actually found it to work well. They may have been insane in other ways, as well. Most people found the conversion to be really bad, and MS subsequently dropped the tool. There is no other good alternative that I am aware of. The two languages are sufficiently different that a good conversion is very unlikely.

That leaves you with a bit of a dilemma, because your choices are realistically these two:

1) Stick with VB6 for that project.

2) Convert it by hand.

That latter option may sound horrible, and it could be if the project is really that big. I've converted over smaller programs, and found that the conversion is pretty quick. FAR quicker than writing it the first time around, but not insignificant, etiher. Most methods would copy over directly, with the only changes being that some types would have to change, most notably the Long in VB6 is now the Integer in .NET, and the Long in .NET is a 64-bit integer, which is almost never needed and comes at a very slight performance cost.

Of course, some things won't convert over all that well. For example, VB6 had to make use of arrays for everything. In .NET, there are the far easier Generics, but there's no straight up conversion. Any time you are calling ReDim or ReDim Preserver, a generic List(of T) would likely reduce the code and improve performance, though the old way still works.

Also, forms are a pretty different animal in .NET. Back in VB6, the form was an odd beast. In .NET, all controls and the form itself are just like any other part of the code. No strange frm files with odd stuff in them. There's just the .designer.vb file that holds all the controls and the form (and which isn't necessary and didn't exist prior to 2005), and the .vb file which holds all the event handlers. Whether there is any straight up form conversion tool, I couldn't say.