Using Future and not using default context with Play framework

I am fairly new to Scala and Play. I have very minimal understanding of ExecutionContext and thread pools, fork-join pools. I will first state the problem I am trying to solve, and then ask my question around it. The Play documentation on this is so terse that I do not even understand the example given on this page about how to create my own pool by configuring the conf file and then using it in my play application.

Problem: In most of our production code we use Future and use the default execution context. I am however writing a new microservice where one of the REST end points has to do a disk IO operation that may take a minute or so in some cases. I have been asked to explore to use some thread pool. Should I use fork-join? FixedThread pool? This is a play application so I went to this page to read the example but I dont understand how the execution context is being created. I am attaching a link for the screenshot from play web page

And this is where I found it
But I am not even able to prototype to see how to test it. Any starting pointers will really help