Lots of Android phones have special ways to trigger Google Assistant, for example, holding down on the home button or pressing a dedicated physical assistant button on the side of the phone.
These are designed to make it really quick to trigger the assistant, but if you don't use Google Assistant (like me), they're a bit of a waste. However, you can make them trigger any app using Assistant Mapper (https://play.google.com/store/apps/details?id=amirz.assistmapper)
You basically set it as your default assistant app, then choose what app you want it to open when it gets triggered. You can set it down to particular screens in each app. At the moment I have it set to Shazam so I can find songs really quickly, but I might change the mapping later.