Send excel data into our XML file

Let's say you have those values in an Excel file under columns A and B, here is how you would update your XML file with that data:
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var workbook = ExcelFile.Load("input.xlsx");
var worksheet = workbook.Worksheets[0];

var xml = new XmlDocument();
xml.Load("box.xml");
var nodes = xml.DocumentElement.ChildNodes.Cast<XmlNode>().ToArray();

for (int index = 0; index < 4; index++)
{
var row = worksheet.Rows[index];
var node = nodes[index];

node.Attributes["X"].Value = row.Cells["A"].Value.ToString();
node.Attributes["Y"].Value = row.Cells["B"].Value.ToString();
}

xml.Save("box-updated.xml");
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The code is processing Excel using this C# library.
Also, you can as a reference this full C# example for reading Excel files.
I hope this helps.