https://learn.microsoft.com/ja-jp/dotnet/api/system.xml.xpath.xpathnavigator.settypedvalue?view=netframework-4.8.1&viewFallbackFrom=net-6.0
XPathNavigator.SetTypedValue(Object) Method (System.Xml.XPath) | Microsoft Learn
Sets the typed value of the current node.
objectmethodsystemxmlxpath