Before I provide you with an answer, I wanted to recommend a slight code change. Since you are setting the Boolean value of pnlInsert.Visible based on a condition, which itself returns a Boolean value, simply get rid of the conditional check in the first place:
pnlInsert.Visible = ChkVul.Checked
Now to your question. What you are essentially asking is how to write a value to an XML file. Something to consider is that XML is only a markup language. At the end of the day, an XML file is simply a file that contains formatted text.
If you do not already have an XML file to read from, simply create a new instance of a XDocument (documentation). If you do have an XML file, then create a new instance of a XDocument by calling the static XDocument.Load method (documentation). Here is a function that takes in a file location and attempts to load a XDocument, if it is unable to then it returns a blank XDocument with a single <root> element:
Private Function LoadOrCreateXml(filename As String) As XDocument
Dim document = New XDocument()
document.Add(New XElement("root"))
Try
If (Not String.IsNullOrWhiteSpace(filename) AndAlso IO.File.Exists(filename)) Then
document = XDocument.Load(filename)
End If
Catch ex As Exception
' for the sake of this example, just silently fail
End Try
Return document
End Function
Now that you have an XDocument, it is just a matter of writing the value. You did not provide any details as to where the value should go or what the tag name should be, so I am going to assume that it should be a child of the <root /> element and the value would look something like this: <ChkVul>true/false</ChkVul>.
To do this, we will need to get the <root /> element by calling the Element method (documentation) on the XDocument to get the element and then call the Add method (documentation) on the resulting XElement to add our node with the value:
Dim document = LoadOrCreateXml("my-xml-file.txt")
document.Element("root").Add(New XElement("ChkVul", ChkVul.Checked))
The final piece of all this is to write the in-memory XDocument back to the file. You can leverage the XDocument.Save method (documentation):
Dim filename = "my-xml-file.txt"
Dim document = LoadOrCreateXml(filename)
document.Element("root").Add(New XElement("ChkVul", ChkVul.Checked))
document.Save(filename)