This approach is only because you wanted to do using javascript. Else it is also possible directly in PAD 😊.

Reading the value in loop, removing first 3 characters in javascript, returning the output and writing to Excel.

Input/Output:

Copy-Paste the below code in your flow editor, change the excel path and run the process
Excel.LaunchExcel.LaunchAndOpenUnderExistingProcess Path: $'''c:\\test\\Excel.xlsx''' Visible: True ReadOnly: False Instance=> ExcelInstance
Excel.ReadFromExcel.ReadAllCells Instance: ExcelInstance ReadAsText: False FirstLineIsHeader: True RangeValue=> ExcelData
Excel.GetFirstFreeColumnRow Instance: ExcelInstance FirstFreeColumn=> FirstFreeColumn FirstFreeRow=> FirstFreeRow
LOOP WHILE (LoopIndex) < (FirstFreeRow)
Excel.ReadFromExcel.ReadCell Instance: ExcelInstance StartColumn: $'''A''' StartRow: LoopIndex ReadAsText: False CellValue=> ValueRead
Scripting.RunJavascript JavascriptCode: $'''var str=\"\";
str = \"%ValueRead%\";
str = str.substring(3);
WScript.Echo(str);''' ScriptOutput=> JavascriptOutput ScriptError=> ScriptError
Excel.WriteToExcel.WriteCell Instance: ExcelInstance Value: JavascriptOutput Column: $'''A''' Row: LoopIndex
Variables.IncreaseVariable Value: LoopIndex IncrementValue: 1 IncreasedValue=> LoopIndex
END
You also have a same post here.
Can you please close the posts.