Translations:Dolphin/File Management/128/en
Alternatively, if you want to change multiple associations right quick, you would edit the *.desktop file directly, e.g. the file /usr/share/applications/org.gnome.Builder.desktop. For example, Gnome Builder associates with a great number of file-types which may not be desirable. So the line
MimeType=application/javascript; # we do not want all of these ....