Unable to add parameters to a variable in a request

I have a scenario where I need to update the request body of a POST request with a response extracted in a variable from a previous request.
However the response from the first request I stored in a variable and while running the next POST request, I am calling the response stored in the variable created, but I need to add few parameters to it before running the request.
Can someone share their thought on how to do this.

Could you visually show an example of this, please?

In your pre request script on the second call you can do something like
pm.environment.set(“variable_key”, pm.environment.get(“variable_key”) + “whateverYouWant”);