How can i customize my shipping rates using USPS?

Checkout the video tutorial below.

Click here to go to the USPS registration page. 
To register for USPS user ID, fill out the USPS webtools registration form on the USPS site which looks like the below screenshot for your reference,

Once the form is submitted. The User ID will be sent to your registered email address and then you can validate that User ID on our app to link your USPS account in our app.

Once the User ID is validated successfully in our app, you can choose your preferred shipping services on our app and you will be able to see the rates from USPS at the checkout page.