Serious question is log in to JPA. You can do this via any RLI enabled portal, for example DII or stand alone PCs often provided in shore establishments.
If you can't access them you can go on to Defence Gateway and download the PDFs of the forms, fill them in and send them off to your UPO/Pay Office. Finally you can ring JPAC and get a lot of things done over the phone. You will need your login name and the security phrase you set on JPA.
JPAC Enquiry Centre,
Mail Point 465,
65 Brown Street,