ninja-forms-settings-permissions.php

<?php
add_filter( 'ninja_forms_admin_parent_menu_capabilities',   'nf_settings_capabilities' ); // Parent Menu
add_filter( 'ninja_forms_admin_all_forms_capabilities',     'nf_settings_capabilities' ); // Forms Submenu
add_filter( 'ninja_forms_admin_settings_capabilities',      'nf_settings_capabilities' ); // Settings Submenu
function nf_settings_capabilities( $cap ) {
    return 'edit_posts'; // EDIT: User Capability
}