I'm assuming that you are attempting to add this information to the Chromatogram view in MassLynx. To do this select Display>View from the chromatogram window, then select the Header button at the bottom.
This will open the "Header Editor". Here you can select the "area" that you want your custom text to be located. The "Cell" tool at the bottom allows you to select what data you would like to display (and the format options). In your case you would select the RawDataDate and/or RawDataTime "Elements" and add them to a cell.
It is also possible to insert free text in any of the cell locations. To do this, select the [Text] Element from the list in the Cell options and add it to the Format Box. This will open the User Text editor.