Depends what type of DLL it is - if it's an "original" DLL then it's not directly usable by VB or any other .NET language: you have to use DLLImport or provide a wrapper class to use it. That can get complex as the datatypes aren't the same in the original C++ and .NET.
If it's a .NET assembly, you can use ILDASM.EXE which is installed with VS in the folder:
C:\Program Files (x86)\Microsoft SDKs\Windows\v10.0A\bin\NETFX 4.7.2 Tools
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--- May be different from here for you - check.
And loading the DLL into the app.