To retrieve a value after using add_settings_field() you should use get_option().
So you could do something like this…
$value = esc_html(get_option('option_name'));
if ($value) {
echo '<a href="' . $value . '">Click Here</a>';
}
You just need to change option_name
to your field name. The code will grab the value and if it isn’t false echo the link. Also added the escaping.
*Updated after OP gave more details