Hi tetiana258,
Thanks for reaching out using Apple Support Communities. Here to help.
We understand you are having trouble deleting a specific application.
Outlook is an application that normally can be removed. Based on what you've described, we wonder if you may have a profile from a workplace, school, or other organization installed?
Install or remove configuration profiles on iPhone
The link above will help with how to remove configuration profiles, which may prevent certain settings from being accessed or changed. Removing the profile should in turn allow you to remove the app.
Let us know if this helps, or if we can help any further.