Please provide a link to a page on your site where we can see this. Thanks.
To hide it, use this CSS:
nav#nav-below {
display: none;
}
To add or override CSS: use the “Additional CSS” option in the customizer. https://codex.wordpress.org/CSS#Custom_CSS_in_WordPress or at [site]/wp-admin/customize.php if you don’t have that menu option.
Use the Chrome Developer Tools or Firefox Developer Tools to help you see and test changes to your CSS.
There may also be tools within your theme, Fluida Plus.
Support of all commercial themes and plugins is out of scope for these forums. While we will not close your post, we also cannot guarantee any support at all, be that by volunteers or the developers. We recommend you instead use the developer’s official contact for their premium offerings, as that is the most direct line..
https://www.cryoutcreations.eu/wordpress-themes/fluida