Ninja Froms permissions for Editors (from https://wordpress.org/support/topic/works-but-there-is-capabilities-problems)

functions.php

function squazz_change_ninja_forms_capabilities_filter()
{
    return 'edit_others_posts';
}
add_filter('ninja_forms_admin_menu_capabilities', 'squazz_change_ninja_forms_capabilities_filter'); // Show Ninja Forms menu
add_filter('ninja_forms_admin_add_new_capabilities', 'squazz_change_ninja_forms_capabilities_filter'); // Show "Add New" submenu
add_filter('ninja_forms_admin_all_forms_capabilities', 'squazz_change_ninja_forms_capabilities_filter'); // Show "All Forms" submenu
add_filter('ninja_forms_admin_submissions_capabilities', 'squazz_change_ninja_forms_capabilities_filter'); // Show "Submissions" submenu
add_filter('ninja_forms_admin_import_export_capabilities', 'squazz_change_ninja_forms_capabilities_filter'); // Show "Import / Export" submenu