Hi there!

Thanks for your query. Please use the following code in your custom CSS:

@media (max-width: 991px){
.nav-placeholder, #sp-header {
    display: block !important;
}
}

Note: Path towards custom CSS(Joomla 3): Extensions>Templates>Styles> Click on your current default template name then choose Template Options. Then find custom CSS within the custom code.

Best Regards

Thanks a lot!