Instead of the default assistant app, you can launch any app on your phone by performing the Assistant gesture (bottom-edge-swipe-up/long press 'home' button) or via the assistant button on some phones (like Samsung)

-- Quick Setup --
- Open 'App Launcher Assistant' app.
- SELECT the app to be launched via the assistant gesture/button from now on.
- [Important] Set App-Launcher-Assistant as the DEFAULT Assist app on your device (see screenshots).

..that's it. From now on, when you perform the assistant gesture/press the assistant button - the app you SELECTED will open up, instead of the default assistant app.

A good use case for this app
- quickly open the CAMERA app with the assistant gesture/button.
- you don't have to stop what you are doing, minimise the current app, go to home screen, and then finally open the CAMERA app from the home screen shortcut (or worse from the app drawer).

Note: This app is open source. Check out its source code here : https://github.com/vinaywadhwa/App-Launcher-Assistant