Navigate to Customization > Navigation. Click the three dot menu to Edit. You can then drag and drop the menu links to change their order or click their three dot menu to Edit their name or URL and select Custom Link.
Insert the link in the following format:
The target attribute specifies that it should be open on a new tab.
For external links use the full path with https.
The syntax is essential, the link doesn't start or end with quotation marks, copy and paste the URL before " target="_blank.
This approach doesn't work to make links open on a new page on our Landing Pages (Beta) feature.