Microsoft Outlook app question

Hello
I installed the Microsoft Outlook app on my iPhone 6S. My Mail provider is TelkomSA and I have a Imap account. When I set-up the account I discovered that the incoming port number shows 993. When using Telkom IMAP the port number for the incoming server must be 143. So I changed it, but can not save this setting. Under the "Edit information settings" I can only find a "Cancel" option. When double tapping on that my choice revert back to 993? Any advice will be appreciated.