test.cs

private void ImportSpreadsheets(string filename, string[] sheetNames) {

   foreach (string sheetName in sheetNames) {
      TXTextControl.LoadSettings ls = new TXTextControl.LoadSettings() {
         DocumentPartName = sheetName
      };

      textControl1.Selection.Load(filename, TXTextControl.StreamType.SpreadsheetML, ls);
   }

}

ImportSpreadsheets("cashflow.xlsx", new string[] { "2021", "2022" });