How can I run a static constructor?

Also you can do this:

type.TypeInitializer.Invoke(null, null);

The other answers are excellent, but if you need to force a class constructor to run without having a reference to the type (i.e. reflection), you can use RunClassConstructor:

Type type = ...;
System.Runtime.CompilerServices.RuntimeHelpers.RunClassConstructor(type.TypeHandle);

Just reference one of your static fields. This will force your static initialization code to run. For example:

public class MyClass
{
    private static readonly int someStaticField;

    static MyClass() => someStaticField = 1;

    // any no-op method call accepting your object will do fine
    public static void TouchMe() => GC.KeepAlive(someStaticField);
}

Usage:

// initialize statics
MyClass.TouchMe();