Convert json to p8 for APN auth key

I was trying to generate the apn auth key from apple dev account. I clicked on the download button and then the downloader downloaded the file as dowload.json format. And When opened the FCM. It requires p8 format. After that I generated another key and got it again as download(1).json. Now i cant generate more keys. How can i convert these two keys to p8 format?