Why my outlook app is not working?

Given that you have not described the problem, except "is not working", then no one could be able to help you.

Read this, Writing an effective Apple Support question. Then come back with a message that meets that criteria.

you expect help without explaining the problem does not help us help you.

Since this is a third party app, here is a link to the developer's support containing a link to open a support ticket:

https://support.office.com/en-us/article/Set-up-email-in-Outlook-for-iOS-mobile-app-b2de2161-cc1d-49ef-9ef9-81acd1c8e234