1. Navigate to chrome://settings/content/notifications. You can also get there by going to settings then content and then notifications, but why not just go directly?
How to disable all notifications
1. Toggle "Ask before sending (recommended)" to Off if you wish to disable all notifications from all sites. After you toggle the switch, the UI will say "blocked." If you don't want to stop all alerts, skip this step.
How to disable notifications from particular sites
1. Scroll down to the "Allow list"
2. Locate the site you want to disallow.
3. Highlight the unwanted site URL and hit CTRL + C (or right click) to copy.
4. Click the three dots and select Remove from the menu.
You will no longer receive alerts from that site, but it could still ask you to sign up again. Let's block it from doing so.
5. Scroll up to the "Block" list and click Add.
6. Paste (or type) in the URL of the site you want blocked and click Add.
Now that site will not only stop sending you notifications, but also stop asking you to sign up for them.