How to select a query response before POST Submit - php

Question

I wanted that when the user will choose which brand the model choices will also show by brand. My question is how can I get the model name base on the chosen brand when It won't show because I needed the response from the first one.
<div class="col-sm">
<form class="needs-validation" method="post" novalidate>
<div class="form-row">
<div class="col-md-6 mb-10">
<label for="validationCustom03">Select Brand</label>
<select class="form-control custom-select" name="brandname" required>
<option value="">Select Brand</option>
<?php
$ret=mysqli_query($con,"select brandName from tbl_brand");
while($row=mysqli_fetch_array($ret))
{?>
<option value="<?php echo $row['brandName'];?>" ><?php echo $brandnameSelect = $row['brandName'];?></option>
<?php } ?>
</select>
<div class="invalid-feedback">Please select Item.</div>
</div>
</div>
<div class="form-row">
<div class="col-md-6 mb-10">
<label for="validationCustom03">Model</label>
<select class="form-control custom-select" name="modelname" required>
<option value="">Select Model</option>
<?php
$ret=mysqli_query($con,"select modelName from tbl_model WHERE brandID='$brandnameSelect'");
while($row=mysqli_fetch_array($ret))
{?>
<option value="<?php echo $row['modelName'];?>" ><?php echo $row['modelName'];?></option>
<?php } ?>
</select>
<div class="invalid-feedback">Please select Item.</div>
</div>
</div>
<div class="form-row">
<div class="col-md-6 mb-10">
<label for="validationCustom03">Item Name</label>
<input type="text" class="form-control" id="validationCustom03" placeholder="Brand Name" name="brandname" required>
<div class="invalid-feedback">Please provide a valid item name.</div>
</div>
</div>
<button class="btn btn-primary" type="submit" name="submit">Submit</button>
</form>
</div>
</div> ```

Answer 1

you must use javascript and you have just 2 choices :
fetch all models when you are loading the form page, then handle their corresponding select boxes options by js based on the selected model.
use ajax on brands select boxes changes event, fetch related model and add them as options to models select box.
you cannot do anything more to achieve this.