How to manually invoke an event?

You can't invoke an event which is owned by another type. An event can only be invoked from the inside the class which declares it.

well i end up here about searching how to simply start event, which is not having any custom args or anything. I know OP question is different! but i had like to share, i hope it helps someone.

Unsimplify version:

 var Handler = EventNameHere;
        if (Handler != null)
        {
            Handler(this, EventArgs.Empty);
        }

Simplify version:

 EventNameHere?.Invoke(this, EventArgs.Empty);

Can it be done using conventional C#? No (as previously stated). But using reflection it is possible. Here is some tested code based on the answer to this MSDN forum thread:

class InvokeFromMe
{
    public event EventHandler RaiseMe;
}

class Program
{
    static void Main(string[] args)
    {
        var fromMe = new InvokeFromMe();

        fromMe.RaiseMe += fromMe_RaiseMe;
        fromMe.RaiseMe += fromMe_RaiseMe1;
        fromMe.RaiseMe += fromMe_RaiseMe2;

        FireEvent(fromMe, "RaiseMe", null, EventArgs.Empty);
    }

    static void fromMe_RaiseMe(object sender, EventArgs e)
    {
        Console.WriteLine("Event Handler 0 Raised");
    }
    static void fromMe_RaiseMe1(object sender, EventArgs e)
    {
        Console.WriteLine("Event Handler 1 Raised");
    }
    static void fromMe_RaiseMe2(object sender, EventArgs e)
    {
        Console.WriteLine("Event Handler 2 Raised");
    }

    public static void FireEvent(object onMe, string invokeMe, params object[] eventParams)
    {
        MulticastDelegate eventDelagate =
              (MulticastDelegate)onMe.GetType().GetField(invokeMe,
               System.Reflection.BindingFlags.Instance |
               System.Reflection.BindingFlags.NonPublic).GetValue(onMe);

        Delegate[] delegates = eventDelagate.GetInvocationList();

        foreach (Delegate dlg in delegates)
        {
            dlg.Method.Invoke(dlg.Target, eventParams);
        }
    } 

}

UPDATE

I'm not familiar with the System.Timer.Timer class, so I'm not sure what is different from my provided example. You could perhaps try something like:

public static void FirePublicEvent(object onMe, string invokeMe, params object[] eventParams)
{
    MulticastDelegate eventDelagate =
          (MulticastDelegate)onMe.GetType().GetField(invokeMe,
           System.Reflection.BindingFlags.Instance |
           System.Reflection.BindingFlags.Public).GetValue(onMe);

    Delegate[] delegates = eventDelagate.GetInvocationList();

    foreach (Delegate dlg in delegates)
    {
       dlg.Method.Invoke(dlg.Target, eventParams);
    }
}