It is not clear, but I suspect you want to insert a new line rather than
just adding one.
If this is so, you are trying to commit spreadsheet, a serious sin in
database.
database data does not have an order. While it may often look like a
spreadsheet with lines of data in the same order as you input the data, but
it may not always be that way. Tomorrow you may find that all those lines
are now in all mixed up in a new order. Consider a table as a bucket of
data not a list.
It the order is important to you then you must add a way of sorting the
data in the order you want it.
You should not even use that table to add edit or view data. It is not
for human consumption it is only there for the program.
If I am right, then tell us in some more detail about your problem and
maybe we can offer some suggestions.