How to have a separate menu for mobile device in Point theme?

My site is idiotdiary.com and I have created two menus namely – “Mobile Menu” & “Primary Menu”- of which I want to set first one as mobile menu and primary menu is the current menu. As the current menu is lengthy I want to set a shorter one for mobile devices.

Below is the current code of header.php. Please suggest me the changes to make for setting “Mobile Menu” as a separate menu that’ll show up in mobile devices only without the current menu i.e. “Primary Menu”

[ Large code block redacted ]