Proxify the request from local browser, modify the response and return back to the browser. How?

Sorry if it was asked before, but Postman’s documenation is almost absent for these matters.
I need to proxify the request from local browser in Postman, modify the response on the fly (just after receiving the response from remote side) and return back the tweaked response to the browser. How to do this? I’m using the latest PM version.
I’ve tried anything possible there with no luck. Im successfuly catching the request/response with Postmans proxy feature but how to tweak the response before sending it back to the browser? I also tried to save the catched request/response and add a test (Tests tab), but the test isn`t called to new request to the same URL.
Such obvious things must be super-easy accessible (as they are in other proxies), without readong whole Internet with no luck…