I know Owlswipe posted a similar question, but it wasn't quite what I was looking for. On my Samsung Galaxy S6, if I hold down the home key, it launches the Google Assistant. Is there a way I could change this so it launches Cortana instead? I was able to do this with a different phone when the assistant was Google now, but I can't find the option for this anymore. Last time, when I downloaded Cortana, and did the shortcut, it would prompt me to change Cortana as the default app for that action, but it didn't do that this time.
Andrew T's answer in the coments ia the answer. To change default apps, including the default assistant, go here: http://www.pocketmeta.com/change-default-apps-android-marshmallow-33779/