In kintone, a school-cap icon appears at the top of the screen during the 30-day free trial period. When the free trial period is over, the school-cap icon automatically disappears from all users' screens.

If you want to hide the school-cap icon during the free trial period, configure not to grant permission to create apps to users. The school-cap icon is not displayed for the users who do not have permission to create apps.
For details on how to configure the permission to create apps, refer to the following page.
Permission to create apps

Note that Users & System Administrators have all permissions for kintone.
Therefore, the school-cap icon is visible to Users & System Administrators even if the permission to create apps is not explicitly granted to them.