How to edit file from WordPress menu

1) Open the WordPress Plugins menu page.

2) Click on "Edit" link under the "Booking Calendar" plugin.

3) On the right side of that page, please find specific file, like this:

booking/css/client.css

Or some other that you require. Click on that link.

4) Make edit of this file.

5) Then click on "Update file" button to save changes.

6) Clear browser cache and test it.