How to find out a password for an old apple ID?

Hello. I was looking for help on how to find the password for an old apple ID. I created a new one some time ago but I still get prompts from my iphone and ipad asking for the password to the old one. I went into icloud setting to delete the old account (which is instructed to do) but it asks for the old password which I have long forgotten. The password will not be sent to email so I really need some help. Thanks.