How to connect to GSX Apple Global Exchange?

You need to be an Apple Authorized Service Provider in order to apply for a GSX account - are you?

https://learn.jamf.com/en-US/bundle/technical-articles/page/Integrating_with_Apples_Global_Service_Exchange_GSX.html

We are other users and cannot help you with that; you need to contact Apple.

I found this explanation online. Hope it helps answer your question.

https://learn.jamf.com/en-US/bundle/technical-articles/page/Integrating_with_Apples_Global_Service_Exchange_GSX.html#:~:text=Go%20to%20http%3A%2F%2Fwww,to%20learn%20more%20about%20GSX

You need to contact the Administrator of the account in your company and they will take care of it.

Here are Apple's rules on how to become an authorized service provider:

Apple Authorized Service Provider Program - Official Apple Support

As I said, we are other users and cannot give you step by step.