Just CLEAR the DATA.
Go To: SETTINGS, APPS, ASSIST, CLEAR DATA.
That will reset ASSIST, and turn it off. The only way to turn it on again, is to open the app, and instruct it to start assisting you.
I have needed to turn off moto assist on my 2nd gen Moto X as it continually announces calls and text messages while I am sitting in a quiet, open plan office - even when set to have no interruptions. I love the moto assist features, but I can not find any other way to stop this one annoying feature. And yes, before anyone suggests it, I have cleared the app data several times and nothing works.
To stop Motorola Assist (called "Moto" on Droid Turbo), simply reverse what you did to activate it. Here are the steps:
1. Go to apps
2. Tap Moto (may be tagged "Motorola Assist" on other phones
3. Tap Continue
4. Answer "No, maybe later" on bottom-left
5. Use back arrow to go back to home screen
I have not fully tested this but it got the Droid Turbo to stop responding to my vocal launch command of "this is your captain" in my case.
Removing the app is not recommended: This may impact execution of other apps. And you may want to run the app later.
They've put stuff in other places. My X Pure came with MM installed and I've disabled Moto.
I'd like to know where some of the features were put, I'd love to tone down the sensor so it doesn' t pick up every movement - even paper. It's nice, but too sensitive. I've searched and most of the answers involve Assist which is not viable on MM. Moto seems more about privacy than customizing.