saved login

hi. I have an old facebook account on an iPhone 5/. I lost the password. The old pw is saved on the old phone and I can automatically access the app on it but I have not been able to transfer it that fb account to my new phone or to find the saved login pw/ Now I am told that messenger no longer works on the old phone. i would like to access the saved login info or change the pw so I can use

my old account on my new phone. Any suggestions/ thanks