After I added a new symbol with Symbol > New,
then go Symbol > Quote editor,
then click on the first row (new) to edit a new quote,
then click on the white area (because there is no existing row),
nothing happened, so I click [OK],
and go back Symbol > Quote editor again, also nothing here,
hope to click on the white area can add a new quote also.
then click somewhere outside of "(new)" row (but inside list).
Note that you can only edit data for databases that are NOT plugin-driven.
If you have problem and quote does not appear, you can switch temporarily the Mode from "Current symbol/all quotes" to "All symbols/single quote" and back.
Doing so should show first record. From then on you should be able to enter all remaining quotes without doing that. Also note that it is easier to import quotes from file than edit them one by one.