I can’t find passcode page

Marking your own post as Solved may prevent others from trying to help because they think you have fixed your problem.

For the passcode, from the related article above.

1. On iPhone X and later, or iPad with Face ID, go to Settings > Face ID & Passcode. On earlier iPhone models, go to Touch ID & Passcode. On devices without Touch ID, go to Settings > Passcode. 

For the Yahoo email, have you looked in Settings/Mail/Accounts?