C# refactoring in class library

in my class library there is a class A have method "Add"

 Class A{
        //method A
        bool Add (string Username, string ItemDescription, int Quantity){
              CheckStock checkStock = new CheckStock();
             if (!checkStock.isAvailble) return false;
             RePositoryA rePositoryA= new RePositoryA();
             if (rePositoryA.GetUserID<=0) return false;
             RePositoryB rePositoryB= new RePositoryB();
             if (!rePositoryA.AddInvoice) return false;
             return ture;
        }
    
}
   class RePositoryA {
         
    //get userID based on username 
          int GetUserID (username){
       //connect to database and get id
   }
    
   class RePositoryB {
         
    //add invoice 
          bool AddInvoice(Invoice myInvoice){
       //connect to database and add invoice to dabase
   }
  

     class CheckStock {
             bool isAvailble(string ItemDescription){
             //connect to webAPi and return if its in stock
         }
      }

 }    

my question is

1. how to refactor the method "Add" so we do not directly instantiate the new RePositoryA , RePositoryB and CheckStock? 2.I know one method do three thing violate "only do one thing policy" so above code might need to breakdown in three methods? Like

      bool Add(){
             CheckStock();
             GetUserID();
             AddInvoice();
   

   }

Thanks for the help !!!