Dear Julie,
please search for the following code in “header.php”:
<a href="<?php echo esc_url( home_url( '/' ) ); ?>"><img class="header-logo" src="<?php echo esc_url($hightide_options_db['hightide_logo_url']); ?>" alt="<?php bloginfo( 'name' ); ?>" /></a>
and replace <?php echo esc_url( home_url( '/' ) ); ?>
with the requested URL address. For example:
<a href="https://www.example.com" src="<?php echo esc_url($hightide_options_db['hightide_logo_url']); ?>" alt="<?php bloginfo( 'name' ); ?>" /></a>
Instead of modifying the theme directly, I recommend you to create a child theme to ensure that your modifications are preserved when you update the original theme.
Best regards,
Tomas Toman