How to Rename a Trailhead Playground in Salesforce

I'm a conflicted in answering this. If I give you too much detail it will make it too easy for others to complete the module (I.e. I shouldn't just dump my entire WarehouseCalloutService implementation). If I give you too little it won't be sufficient to answer your question.

My suggestions that hopefully find the right balance:

1. Use https://json2apex.herokuapp.com/ to get the definition of the Equipment that you can parse from the JSON.
2. Examine what is generated by the API and figure out what you do and don't need. You might not need all the fields the JSON returns. Cough Maybe even ones that are a bit problematic Cough.
3. There are some really good examples of how to parse a JSON string and Deserialize it into objects in the docs.

From my pass through the badge I didn't encounter the problem you are having with the name. Maybe double check your code that is altering the _id values? I didn't need to do any post processing on the JSON response. It went fine as direct input into the JSON parsing.

From the Welcome tab there is link to get the credentials which you can use to get credentials.

Long story short Go to your user > Confirm your email is correct and click on Reset password link and you will get the Rest password link where you can reset the password.

Details Step by Step