iTunes' instructions can be found HERE
Google's instructions can be found in the "Restart or re-subscribe to a subscription" section of THIS PAGE 

If your subscription was bought on the PNP website, you can re-enable the auto renewal in the same place you turned it off:
1. Log in to your PNP account on the website
2. Go to My Account
3. At the bottom of the page, click the button to renew your subscription