If you have accepted push notifications through your computer or phone, depending on the browser you use, you can follow the below steps:

Chrome: 

1. At the top right, click Settings
2. At the bottom, click Advanced
3. Click Site settings, under "Privacy and security" 
4. Click Notifications
5. Choose to block or allow notifications, block all: Turn off 'Ask before sending'

Firefox:

1. Right-click (on Mac, Ctrl+click) a blank area of the page and choose 'View Page Info'
2. (menu bar) Click Permissions
3. Click Block

Edge: 

1. At the top right, click Settings
2. Scroll down and click on “View advanced settings” button
3. Click off on the 'Block pop-ups' slider

Safari:

1. Open Safari Preferences from the Apple menu
2. Select 'Websites'
3. Select 'Pop up Windows' on the left
4. Select Block in the 'When visiting other websites' drop down