How to iterate over multimap of struct C++ [closed]

I have a multimap of struct. How to iterate and get the Struct member value "scale" using the key "sourceID".

std::multimap<std::string /*sourceID*/, NumData> numDataMap;
    
struct typeData
{
   float value;
   std::string uom;
   float scale;
};
struct NumData 
{
   std::string cardinality;
   std::map<int/*cardinality*/, std::map<type, typeData>> dataMap;
};

Please suggest any alternate design how to containerize the above data.