What do you mean by turn it off? You mean turn off notifications? Go into the settings on your phone, go to digital well being and parental controls, then click on the 3 dot menu on the upper right and go to settings, select notifications and turn off notifications.
If you are requesting something else, please be more specific on what is happening. As far as I know, Digital well being is on all the time in the background and you can check your statistics at any time. I've never been bothered by anything relating to it, even though notifications appear to be enabled. Perhaps it's because I never set any goals for it to nag me about.
