but it doesn’t work :(

Wow. Are you trying for an award for tersest question?

See this FAQ: https://notepad-plus-plus.org/community/topic/15739/faq-desk-request-for-help-without-sufficient-information-to-help-you

Based on the brief description of your problem, I am guessing that the following would be of use for helping us help you: Notepad++ information (version, location, plugins, etc – all of which can be gotten by pasting the Debug Info, as described in the FAQ), the name and location of the file you are trying to edit, your exact steps when you edit (a hint: any configuration file edit needs to be followed by exiting notepad++ completely), what you expect to happen by making this edit vs. what actually happened.

Also, please clarify whether you actually used smart quotes, like the forum shows, or whether you used real ASCII quote marks. Because if there are really smart quotes, that’s not valid XML, and the config parser won’t understand it.