Your example does not contain any data so it is not easy to interprete.
If you want to collect lines and add them at the bottom of your sheet that is not possible with standard Excel nodes. You would have to collect the data first or revert to some Python things with openpyxl - but that might be overengineered.
To collect data you could ‘append’ them to a KNIME table like in this example:
Or you could use the recursive loop