How can I set up a hyperlink in the menu?

How can I set up a hyperlink in the menu?

Hey, I'm building a personal page and I selected a template with a simple menu, just the links on the upper-right corner. And I would like to set up the "Contact" link as a mailto link to open the user default mail client. I tried looking in the HTML/CSS editor but I couldnt find the code for that part of the website anywhere. Can someone help me?