Q:

How can I trigger Parent form event from Child form?

I have a parent form from which I create and instance of another form.(child form)
I am trying to trigger an event on the parent form from the child form. 
(I have tried reading a few similar questions on SO but they were either in c# or had too little explanation for a rookie like me. 
Parent Form:
Private Sub DataGridView1_CellContentClick(ByVal sender As System.Object, ByVal e As System.Windows.Forms.DataGridViewCellEventArgs) Handles DataGridView1.CellContentClick

            Dim index As Integer = Convert.ToInt32(DataGridView1.CurrentCell.RowIndex)

            Dim frmjvauth As New frmjventry_Auth
            frmjvauth.Show()
            frmjvauth.txtjvnumver.Text = DataGridView1.CurrentRow.Cells("jvnumber").Value
            frmjvauth.showjv()
    End Sub

Private Sub child_Change(sender As Object, e As EventArgs)
        MsgBox("hey")
    End Sub

Child Form:
Private Sub frmjventry_Auth_FormClosed(sender As System.Object, e As System.Windows.Forms.FormClosedEventArgs) Handles MyBase.FormClosed
    RaiseEvent child_Change(Nothing, Nothing)
End Sub

A:

Triggering an event from outside of your class is dependent to implementation of your event and your class.
An event raise when a specific case happens, for example when changing a property value, when click on a button and so on. To trigger that event, you should simulate that happening, for example, you should set a value for the property that you want to fire its change event or for example for a button, you should call PerformClick method of that button.   
But in general, it's better to create a public method in your parent form and put your logic there and call that method from outside of the form.
For example I suppose you need to trigger Click event of button 1 and have this code:
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
    //Some logic here
End Sub

Option 1
You can add a public method and move your logic there and also call that method in button1_Click:
Public Sub MyLogic()
    //Some logic here
End Sub

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
    MyLogic()
End Sub

then from outside, you can simply use the logic this way:
//I suppose f is an instance of your form
f.MyLogic()

Option 2
You can make your Button1 public, go to designer and select your Button1 and set value of Modifier property to public. Then you can use this code from outside of your form:
//I suppose f is an instance of your form
f.Button1.PerformClick()

Option 3
For your hand made events you can create a public method in your form that raise your event:
Public Event YourEvent()

Public Sub OnYourEvent()
    RaiseEvent YourEvent()
End Sub

And then use it outside of form this way:
//I suppose f is an instance of your form
f.OnYourEvent()

Sample
Here is a sample containing 2 forms:
'Here is the code for parent form
Public Class ParentFormClass
    Public Sub MyLogic()
        MessageBox.Show("My Logic is Running!")
    End Sub

    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        MyLogic()
    End Sub    

    'This is the way that you pass an instance of parent to child
    Private Sub ShowChildFormButton_Click(sender As Object, e As EventArgs) Handles ShowChildFormButton.Click
        Dim f As New ChildFormClass(Me)
    End Sub
End Class

'Here is the code for child form
Public Class ChildFormClass
    Private MyParentForm As ParentFormClass

    Public Sub New(form As ParentFormClass)
        ' This call is required by the designer.
        InitializeComponent()
        ' Add any initialization after the InitializeComponent() call.
        MyParentForm = form
    End Sub

    Private Sub CallParentFormMethodButton_Click(sender As Object, e As EventArgs) Handles CallParentFormMethodButton.Click
        MyParentForm.MyLogic()
    End Sub 
End Class

