Sometimes automatically asking the user to subscribe for push notification too early can be counter-productive. Here are a few alternatives to that:
Ask visitors to subscribe only after clicking on a button or link. To do so, you must call a certain JS method on click. More info can be found here.
Ask visitors to subscribe after spending a custom number of seconds on your website.
Ask visitors to subscribe after visiting your website a number of times.
All the above options can found if you go to your Dashboard on getpushmonkey.com and, from the left navigation menu, click on "General Settings". Now scroll down to the "Asking to Subscribe" section. Select the desired option and click "Save".