Write a PHP Script in order to show content of etouches in wordpress

I need a php scribt on a wordpress site that shows the content of etouches.

etouches is a event management system. unfortunalty they have limited design options. To solve the problem i want to use wordpress and build a registration site. I already have set up a wordpress site and want to show the content from etouches there per api. https://www.eiseverywhere.com/ehome/developer/home

I use ninja as a form tool and want to reprocude the etouches registrations prozess with ninja form.
What you need to do.

Scribt
1.) a User type in the email adresse in a ninja field. He press submitt and will recieve pre load data from etouches.
2.) He can now edit his data and send it back to etouches per webhook.

You only need to write it for one field. I can copy and paste the rest for other fields.

Best Regards
chris