Hi there, I´m Ivania and I´m glad to help you today.
In Outlook for IOS, if you want to change your account password, it will only be able to change your Office account password in the browser desktop or in the phone browser.
You can go to email on the web to change it.
You can go to:
http://www.office.com/signin
Setup > Password > Make your changes and click Save. You can browse this link on your phone to change the password aswell.
If you want to change the password in the Outlook app for IOS, you can leave your feedback on uservoice:
https://outlook.uservoice.com/
After changing the password, you can update your Outlook password on your Apple iOS:
https://csuf.screenstepslive.com/s/12867/m/5289...
Note that the website I mentioned is not a Microsoft website, but it does appear to contain accurate information and not potentially unwanted applications. It can, however, contain advertisements and use cookies, so be aware.
My best regards,
Ivania
