Unable to insert/or replace value in XML data with condition salary

UPDATE user_details
SET xml_data.modify('insert 2 into (/user)[1]')
WHERE salary = 420000

try this code,  you shold have xml data has a column for this solution to work

string path = AppDomain.CurrentDomain.BaseDirectory + "\\test001.xml";

            XDocument doc = XDocument.Load(path);

            var nodes = doc.Root.XPathSelectElements("//Employee").ToList();

            for (int i = 0; i < nodes.Count; i++)

            {

                if (nodes[i].Element("Salary").Value.ToString() == "XYZ")

                {

                    nodes[i].Element("Tax").Value = "new value";

                }

            }

            doc.Save(path);

Try this code