JSFiddle - React, Tailwind, and code Playground

HTML

<h2>Please fill in the information below</h2>
            <form action="pmUnitCreate.php" method="post">
                <p>Click the Add button to add a new row. Click the Delete button to Delete last row.</p>
                
                <input type="button" id="btnAdd" class="button-add" onClick="addRow('myTable')" value="Add"/>
                 <input type="button" id="btnDelete" class="button-delete" onClick="deleteRow('myTable')" value="Delete"/>



                <br>

                <table id="myTable" class="form">
                    
                     <tr id="heading">
                    <th><b><font size="4">Job Number</font></b></th>
                    <th><b><font size="4">Unit Number</font></b></th>
                    <th><b><font size="4">Job Code</font></b></th>
                    <th><b><font size="4">Model Number</font></b></th>
                    <th><b><font size="4">Scope</font></b></th>
                    </tr>   
                                     
                    <tr id="tableRow">
                        <td>
                            <input type="text" name="JobNumber[]" value="<?php echo $JobNumber;?>" readonly>
                        </td>

                        <td>
                            <input type="text" name="UnitID[]" value="<?php echo $JobNumber;?>-01" readonly>
                        </td>
                        
                        <td>
                            <select name="JobCode[]" style="background-color:#FFE68C" required>
                            	<option></option>
                            	<option>F</option>
                            	<option>FS</option>
                            	<option>PD</option>
                            	</select>
                        </td>

                        <td>
                            <input type="text" name="ModelNumber[]" style="background-color:#FFE68C" required>
                        </td>
<!--
			<td>
			    <form...

CSS

.dropdown-check-list {
  display: inline-block;
}
.dropdown-check-list .anchor {
  position: relative;
  cursor: pointer;
  display: inline-block;
  padding: 5px 50px 5px 10px;
  border: 1px solid #ccc;
}
.dropdown-check-list .anchor:after {
  position: absolute;
  content: "";
  border-left: 2px solid black;
  border-top: 2px solid black;
  padding: 5px;
  right: 10px;
  top: 20%;
  -moz-transform: rotate(-135deg);
  -ms-transform: rotate(-135deg);
  -o-transform: rotate(-135deg);
  -webkit-transform: rotate(-135deg);
  transform: rotate(-135deg);
}
.dropdown-check-list .anchor:active:after {
  right: 8px;
  top: 21%;
}
.dropdown-check-list ul.items {
  padding: 2px;
  display: none;
  margin: 0;
  border: 1px solid #ccc;
  border-top: none;
}
.dropdown-check-list ul.items li {
  list-style: none;
}

JavaScript

function incrementUnitId(unitId) {
  		var arr = unitId.split('-');
  		if (arr.length === 1) {return;} // The unit id is not valid;
  		var number = parseInt(arr[1]) + 1;
  		return arr[0] + '-' + (number < 10 ? 0 : '') + number;
		}

	function addRow() {                
  		var row = document.getElementById("tableRow"); // find row to copy
  		var table = document.getElementById("myTable"); // find table to append to
  		var clone = row.cloneNode(true); // copy children too
  		row.id = "oldRow"; // We want to take the last value inserted
  		clone.cells[1].childNodes[1].value = incrementUnitId(clone.cells[1].childNodes[1].value)
  		table.appendChild(clone); // add new row to end of table
		}


	function deleteRow() {
  		document.getElementById("myTable").deleteRow(-1);
		}

var checkList = document.getElementById('Scope[]');
var items = document.getElementById('items');
        checkList.getElementsByClassName('anchor')[0].onclick = function (evt) {
            if (items.classList.contains('visible')){
                items.classList.remove('visible');
                items.style.display = "none";
            }
            
            else{
                items.classList.add('visible');
                items.style.display = "block";
            }
            
            
        }

        items.onblur = function(evt) {
            items.classList.remove('visible');
        }