Creating unique order id.

Create an `ORDER ID` for gravityform.

Here are the detailed steps on how to add/create a unique order id for specific form.
An order id can be of any format, for demonstration purposes our format would be,
XXX-AAAYYMMDDHHMMSS - change XXX and AAA to your own preferences.

Step 1: Create new form.

Step 2: Add single field
  Label: ORDER ID
  Goto Advance Tab -> Visibility -> Administrative
  
Step 3: Add single field (This will be the $agent value)
  Label: Agent

Step 4: Save the form, Your Done!

Please see also the screenshot in comment.

How it works?
# OrderID field will be populated dynamically before the form is saved to the database

Note: In the code above filter is executed for all submitted forms, but can also be specified
by adding the specific form id on the filter.

Example: 
// Generate OrderID for FormID 12 only
add_action('gform_pre_submission_12', 'your_custom_callback');
function your_custom_callback( $form ) {
  $_POST['input_10'] = 'I love Gravity Form';
}

Reference: https://www.gravityhelp.com/documentation/article/gform_pre_submission/

gform-create-orderID.txt

// Code Placement: current themes functions.php

/**
 * Generate order id for each form [formid, orderfieldID, formname ]
 * [21 383 BLUE] | [10 279  BS] | [22 430  T4] | [23 337  T1]
 */
add_action('gform_pre_submission', 'generate_order_id');
function generate_order_id ( $form ) {
    $form_id = $form['id'];
    $agent = strtoupper( substr( rgpost('input_1'), 0, 3) ); // return first 3 characters of the given input 
    $date_time = date('ymdHis', current_time('timestamp')); // returns YYMMDDHHMMSS format (eg.: 170901230000)

    if ( $form_id == 21 ) {
        $_POST['input_383'] = 'BLUE-' . $agent . $date_time;
    } elseif ( $form_id == 10 ) {
        $_POST['input_279'] = 'BS-' . $agent . $date_time;
    } elseif ( $form_id == 22 ) {
        $_POST['input_430'] = 'T4-' . $agent . $date_time;
    } elseif ( $form_id == 23 ) {
        $_POST['input_383'] = 'T1-' . $agent . $date_time;
    } else {
        # do nothing
    }
}

SETTING UP THE GRAVITY FORM:

Screenshot