If Inbox was added by your administrator, you may not be able to remove it.
If you installed it from app store or manually, follow the steps below to uninstall Inbox.
In your preferred browser, go to https://aka.ms/olksideload. This opens Outlook on the web, then loads the Add-Ins for Outlook dialog after a few seconds.
Click on My Add-ins.
In the Store Add-ins or the Custom Add-ins section, click on the … menu on Inbox.
Click Remove. Inbox should now be uninstalled the next time you start Outlook.