add to existing data in a Base table with either Excel or csv
If data are in a base table go to the tables pane. If query then go to the queries pane.
Click over the table/query with secondary button of the mouse. Copy(without open it).
Go to the calc sheet, to the firts cell and paste, and that’s it!
Open the csv file in Calc. From there you can copy and paste into a Base table - either creating a new table or appending the data to an existing table.
See the following answers (first also has link to documentation):