Retrieve details by transaction_id after submission gravity froms

I'm using Gravity Forms for payment section on my website. Once I fill all the data and submit the form, It passing the values to Paypal. After payments completed, It redirects to my website again. What I need is, I should show the user details and payment details on this page if payment status is success. I can get the transection_id by GET method.

$transection_id = $_GET['st'];

How can I get the details by using this $transection_id. Already the details are in the database now. I don't no how to query database. Can I use hooks for this?

add_action("gform_after_submission_5", "after_submission", 10, 2);