Can you describe the data flow a bit more?
"in MATLAB Simulink via ThingSpeak Cloud from MIT APP Inventer Application "
What is the MIT App interacting with? Is it a deployed simulink model on hardware?
The MIT app will support POST commands (I'm pretty sure), you can post to you channel using the REST API write endpoint. You can update multiple fields simultaneously.
You can also use the GET command and append additional fields
Similarly, you can read the whole feed (all fields ) at once with read data. I would use the JSON format, then you can parse the response for the fields you want.