Hey Guys, I found the solution!
1.
Open the file site_root_address\wp-content\plugins\site-layout-customizer\sitelayoutcustomizer.php
2.
Search for Line $tabs = array( ‘1’ => ‘Layout 1’, ‘2’ => ‘Layout 2′,’3’ => ‘Layout 3′,’4’ => ‘Layout 4′,’5’ => ‘Layout 5′,’0’ => ‘Main Options’);
This line is responsible to add more tabs/layouts, just add ‘5’ => ‘Layout 5’, as obove, to add new tab
3.
Search for the line : register_setting( ‘slc_options_4’, ‘slc_options_4’, ‘slc_options_validate’ );
Now INSERT the new line : register_setting( ‘slc_options_5’, ‘slc_options_5’, ‘slc_options_validate’ );
Your 5th layout is ready to use, if you need more tabs, repeat the process. Thanks for the developer of this plugin it’s amazing!!