How to update a row in excel spreadsheet, not add a new one

Question

Following the Graph V5.x updates and the 'code breakers' widely discussed on this forum and others, I've been trying make to get my previously working C# code working again, one part of which is intended to update specific rows in an excel spreadsheet as and when changes on the system occur. I have got very close but I am struggling now to get the code to update the existing row at index i and not insert a row at index i and shift what was the existing row down one in the spreadsheet to row index i+1 .

Is updating no longer possible?

Code format I am using is:

var requestBody = new AddPostRequestBody
{

Index = {targetRow},

Values = new UntypedArray(new List