How do i rewrute urls to be able to use polish?
Polish works by compressing JPEG, PNG, and GIF files. As long as your URL points to a file with one of these formats and with its respective file extension, and as long as you have Polish enabled, it should apply without any need to rewrite the URL.
How can i check if its working?
You need to visit the page with Dev Tools open (F12) or use whatever tools you have to check the headers that come with the image file.