Customize wordpress plugin

Hello, I am seeking to add additional functionality to a Wordpress plugin (Give Donations)

If you look at this code snippet: https://github.com/impress-org/give-snippet-library/blob/master/form-customizations/populate-amount-name-email-from-url.php It pre-populates the Give donation form with user's email/name etc.

I am using a Give add-on plugin that contains custom form fields. I need someone who can customize the script so that instead of user's name / email, I can pre-populate the custom fields in my donation form (based on URL variables) so a URL like this: domain.com/sponsor-a-dog/?dogsname=Test&dogsurl=test.com

I've tried to customizing the code snippet myself with data from my custom fields, but I've had no success as I'm not experienced enough. Thanks