You'll need to identify which giving platform you have been making your donations through. The best way to do this is to look at a recent receipt or the confirmation email issued when you signed up.  

Using the receipt, identify which platform is processing your regular giving. 

MyCause receipts include a teal banner and MyCause logo at the top of the email.

GiveEasy receipts include an "About GiveEasy" section towards the bottom of their receipts.

Let's face it, over the years many of us have accumulated a couple of email accounts, but you will need to know which email account was used to set up the Regular Giving.