if ($existing_value eq "option1") then {
    $html .= qq|
        <select name="my_parameter">
            <option value="option1" selected>Option 1
            <option value="option2">Option 2
        </select>
    |;

} elsif ($existing_value eq "option2") then {
    $html .= qq|
        <select name="my_parameter">
            <option value="option1">Option 1
            <option value="option2" selected>Option 2
        </select>
    |;

}