Add Custom External Link to SharePoint Site Navigation

Steps:

1. Login to your SharePoint Site where you want to add the external link.
2. On the left Navigation list at the bottom you will see a Edit button, click on it,
   
3. Now hover over the navigation links, you should see a horizontal ruler with a + sign, click where you want to stack the link.
   
4. A pop-up will be shown where you can add the details
   • Choose an option: Link.
   • Address: Web Address.
   • Display name: Name as displayed for the Link.
   • Open in a new tab: To open the link in a new tab.
   
5. Click OK
6. You should now have the link displayed on the Navigation Menu.