I think you’re confusion Structs and Data Tables.
Structs don’t have rows to access like data tables. A struct is just a condensed data structure and data tables have rows of data of the same data structure.
If you want to access a member of a struct you would just do this:
ItemFashion.SkeletalMesh = nullptr;
You can use your custom struct for a data table though. I’m not sure what your use case is here so I’m going to point you to this resource which I’ve found helpful for using data tables in C++: Unreal Engine C++ Fundamentals – DataTables – Jolly Monster Studio