where is the value of $USE_GROUP_TABS and which file,
how i can find this means
plz help

This is an old question but here is the solution:

To disable menu groups we can do it via the theme configuration

You need to set β€˜group_tabs’ => false , in a upgrade safe way ( file - custom/themes/SuiteP/themdef.php ) for a particular theme.

    'group_tabs' => false,   //Check this line
    'classic' => true,
    'configurable' => true,
    'config_options' => array(