Hi Linda, do you mean the Face ID or passcode lock?
If yes, open Outlook, tap your profile, go to Settings, then Privacy, and turn off Require Face ID or Require Passcode. If the option is greyed out, your work or school account controls it and you need to contact your IT admin.
If you mean removing the Microsoft account sign in, Outlook for iOS requires you to stay signed in. There is no option to turn that off.