Safari allows you to manage notifications from the browser and System Preferences. With Safari open, navigate from the macOS top menu and select Safari > Preferences > Websites > Notifications to view all the websites you have either allowed or denied notification permissions.
Use the drop-down menu for each entry to change permissions, or highlight a website and click Remove to delete it altogether.
For Mac users you can turn off push notifications via the System Settings menu as well.
On your Mac, choose Apple menu > System Settings, then click Notifications in the sidebar. (You may need to scroll down.)
Go to Application Notifications on the right, click the website, then turn off Allow Notifications.
The website remains in the list in Notifications settings. If you want to remove it from the list, deny the website permission to send notifications in Safari settings.