Hey i would not recommend you to do this because this can lead you into problems for future updates however if you want to add custom Field.
You can do this way.
Edit file >> computer-repair-shop >> lib >> includes >> wc_jobs.php
Now to display custom field.
There are two meta boxes Job Details main metabox
Order Informaiton Sidebar Form
Now decide where you want to add your custom field and add an input field there just like device_id
$content .= '<div class="cell small-6">';
$content .= '<label>';
$content .= esc_html__('Device ID/IMEI', 'computer-repair-shop');
$device_id = get_post_meta($post->ID, "_device_id", true);
$content .= '<input type="text" name="device_id" value="'.esc_html($device_id).'" />';
$content .= '</label>';
$content .= '</div>'; //Column Ends
You can copy same and just change _device_id and device_id and $device_id to your new field name.
You can find those lines in this function >> wc_jobs_features_callback
Now to save it. Just go to
Function and just add new field name in this array below device_id
$submission_values = array (