Hello,You have 2 options:
1) you may write a letter to the Home Office asking for renewal of your PR card. You do not need to fill in a form for this;
2) you may apply using the EEA3 (if you are an EEA national) or EEA4 form (if you are a non EEA national).
The address to send your application (if by letter or using the form) is the same as what is stated on the form.You need to make sure that you have not been away from the UK for more than 2 years in order to qualify for a new PR card.Hope this helps