JSFiddle - React, Tailwind, and code Playground

HTML

<select id="AboveOrBelow" name='AboveOrBelow'>
            <option value=''>Select Above/Below</option>
            <option value='1'>Above</option>
            <option value='2'>Below</option>
          </select>
<select id='InitialLeakSource' name='InitialLeakSource'>
            <option value=''>Select Initial Leak Source</option>
            <option data-aob='Above' value='1'>Above1</option>
            <option data-aob='Above' value='2'>Above2</option>
            <option data-aob='Below' value='3'>Below1</option>
            <option data-aob='Below' value='4'>Below2</option>
          </select>

JavaScript

$('#AboveOrBelow').on('change', function(){
    if($(this).val() === '1') {
        $('#InitialLeakSource option[data-aob=Above]').show();
        $('#InitialLeakSource option[data-aob=Below]').hide();
    }
    else if($(this).val() === "2"){
        $('#InitialLeakSource option[data-aob=Above]').hide();
        $('#InitialLeakSource option[data-aob=Below]').show();
    }
    else {
     $('#InitialLeakSource option').show();
    }
});