1. You can do it yourself, as I understand well that you know coding quite well. Go to Theme Folder and open landing-header.php file. From Line#131-237 is for menu. Cut the code block and place it to about Slider means below Line#112.
2. To make Navbar fixed. You’ve to touch header.php file and functions.js file on line#10-16.
If you face any problem then send your FTP and WP access, I will resolve your problems.