I was able to do this by selecting "All" located under the "Keys" header from the left column
Then I clicked the plus button in the top right corner to add a new key
Enter a name for your key and check "APNs"
Then scroll down and select Continue. You will then be brought to a screen presenting you with the option to download your .p8 now or later. In my case, I was presented with a warning that it could only be downloaded once so keep the file safe.