How To Change Google Assistant Button. First you have to turn assistant off from the settings and then install a button mapper to customize. Activate your Google Assistant by saying OK Google or long-pressing the Home button.
Tap on Settings followed by Settings listed under the Google Assistant label. Thankfully you can disable this feature. I have customised the assistant button to take screenshots splitscreen for supported apps and toggle flashlight.
Whether you do the above or not.
Tap on Settings followed by Settings listed under the Google Assistant label. Get started with the Google Assistant on your Pixel 4 and later. Under Application Manager - Default Apps - Assist Voice Input you can change or turn off you assist app. Thankfully you can disable this feature.