Write value to specific cell to Workbook with VBA code using VB.NET

I have code in Excel VBA that finds a specific value in column 2 and writes the value in that found rows column 3:

ThisWorkbook.Worksheets("Sheet1").Cells(Cells.Find("ProjectNumber", lookat:=xlWhole).Row, 3).Value = "TEST"

I am trying to get that function to run from my Visual Studio application.

Imports Excel = Microsoft.Office.Interop.Excel
Module Automate_Excel

Public xlApp As Excel.Application = Nothing
Public xlWorkBook As Excel.Workbook = Nothing
Public xlWorkSheet As Excel.Worksheet = Nothing
Sub Excel_FinishProject()

    xlApp = New Excel.Application
    xlWorkBook = xlApp.Workbooks.Open("G:\100 Databases\Projects Schedule.xlsx")
    xlApp.Visible = True
    xlWorkSheet = xlWorkBook.Worksheets("sheet1")

'Write
    xlWorksheet("Sheet1").Cells(Cells.Find("ProjectNumber", lookat:=xlWhole).Row, 3).Value = "TEST"

    xlWorkBook.Close()
    xlApp.Quit()
End Sub

End Module

It is giving me errors like

xlwhole is not declared

and

cells is not declared

My understanding is it should be coming from the type library of Excel and code such as:

xlWorkSheet.Cells(2, 5) = "TEST"

which does use "cells".

You need to fully qualify each enumeration. In this case,

Excel.XlLookAt.xlWhole 

XlLookAt enumeration (Excel)

In an Excel/VBA environment, they are just a basic enumeration.

Cells in your code is also not fully qualified. Cells.Find needs a worksheet qualifier. VB.NET does not know what Cells is without a qualifier. Again, in a VBA environment, you do not have to be this explicit, but in VB.NET you do, as there is no "default context"

Your xlWorkSheet variable is not indexed. It's already holding a single reference to xlWorkBook.Worksheets("Sheet1") - So you don't specify the name of it again.

Also, you should store the result of the Find in a Range variable before using it instead of trying to do it all in one line. Then you can check to see if it "didn't find anything" before you try to use the result, and can even see what the result is before taking action

xlWorkSheet = xlWorkBook.Worksheets("Sheet1")
Dim result as Excel.Range = xlWorkSheet.Cells.Find("ProjectNumber", lookat:=Excel.XlLookAt.xlWhole)
If result IsNot Nothing Then
    ' xlWorkSheet.Cells(result.Row, 3).Value = "TEST"

    ' OP says this works instead
    xlWorkSheet.Cells(result.Row, 3) = "TEST"

End IF