Вы можете сделать что-то вроде ниже:
document.addEventListener('DOMContentLoaded', (event) => { // on DOM loaded
var p1 = 'john';
var p2 = 'marcus';
var p3 = 'anthony';
var p4 = 'aaron';
var list = [p1, p2, p3, p4]; // put the variables in a list
var select = document.getElementById("dropTest"); // get the select
var options = select.querySelectorAll("option"); // get it's options
options.forEach(function(el, i) {
if(list[i]) { // if list has element list[i]
el.value = list[i]; // assign option value to list[i]
// commenting out because OP wants only values assigned and not innerHTML
// el.innerHTML = list[i]; // assign option innerHTML to list[i]
}
});
})
<select class="dropwdown-test" id="dropTest">
<option>Person 1</option>
<option>Person 2</option>
<option>Person 3</option>
<option>Person 4</option>
</select>