You can sign in to 1SE on iPhone or Android three ways: email and password, Sign in with Apple, or Sign in with Google. On Android there's no Sign in with Apple, so only email and Google are offered there. 1SE has never had Facebook sign-in; if you remember Facebook, the account was created another way.
Important: signing in with a different method than the one you created your account with opens a new, empty account. If your projects are missing after you sign in, sign out and try the method you used originally. Nothing has been deleted.
Created your account with Apple and moving to Android? Give it a password first: go to me.1se.co/account/reset-password, enter your 1SE account email (tap your profile in the app to see it), then sign in on Android with that email and your new password. The Forgot your password? link on the Android sign-in screen opens the same page.
To change the email on your account, edit your profile in the app after signing in; we can't change it for you.