Call Instance Method From Static Method (C#)

[mcfly1204]

I have two classes in the same namespace, Form1 and NewAccount. I am attempting to call an instance method that will reload a combobox on Form1. I have Form1 implemented as a singleton, and a static method in Form1, but I cannot access the instance method 'LoadAccounts()' which will reload the combobox.

public static void SetAccountID(string account)
        {
            Form1._instance.Show(); //checks for an open instance
            Form1.LoadAccounts(); //not sure how to/if I can call instance function          
        }

My understanding of the singleton pattern was that the call

Form1._instance.Show();

would check for an existing instance, and if one is not present, the class would be instantiated.

public Form1 Instance
        {
            get
            {
                if (Form1._instance == null)
                {
                    Form1._instance = new Form1();
                }
 
                return Form1._instance;
            }
        }
 
private static Form1 _instance = null;

If this means that Form1 will always exist when this is called, I thought I would then be able to call any instance method of that class, which does not seem to be the case. Can I simply not call instance methods from a static method?

[mcfly1204]

After firing this line of code in the static method

Form1._instance.Show();

how do I access this instance, i.e., how do I call instance method for this instance? Am I even on the correct path, or is my line of thinking off on this?