Whether you are on Windows or macOS, it is possible to reset Microsoft Outlook settings to return the program to its original state. The easiest way to do this is to create a new profile and set it as the default profile.
Steps
Method 1 of 2: Reset Outlook on Windows

Step 1. Open the search bar
Click on the magnifying glass or the circle on the right of the menu To start up.

Step 2. Find the Control Panel
Type control panel in the search bar. A list of results will then be displayed.

Step 3. Click Control Panel
This will redirect you to the Windows Control Panel.

Step 4. Find Outlook
Type mail in the Control Panel search bar. It is located at the top right of the window.

Step 5. Click Mail (Microsoft Outlook 2016)
The version number may be different on your computer.

Step 6. Click Show Profiles
The button is located under the heading Profiles.

Step 7. Click Add
This is the first button in the list Profiles.

Step 8. Name the profile
Enter a name for the new profile, then click OK. The name of the profile will appear in the field Profile name.

Step 9. Enter your information
Fill in your account details, then click Next. You must enter the username and password you use to connect to your mail server. Outlook will then try to connect to the server.

Step 10. Validate the modification
If prompted, enter your Windows password, then click OK. If you don't see this option, go to the next step.

Step 11. Click Finish
The button is located at the bottom of the window. This will save your new profile.

Step 12. Select the profile
Click Always use this profile, and then select the new profile. Outlook will open by default with the new blank profile.

Step 13. Click OK
Your settings are now saved. When you open Outlook, you will see that all settings have been reset. Your email and calendar will synchronize with the server and you will be able to access your messages.
Method 2 of 2: Reset Outlook in macOS

Step 1. Open Finder

It is the first icon on the Dock.
To reset Outlook settings in macOS, you will need to create a new profile

Step 2. Open the Applications folder
Double click on the Applications folder. The list of programs installed on your computer will then be displayed.

Step 3. Open the menu
Press Ctrl and click Microsoft Outlook to display the menu.

Step 4. Click Show Package Contents
Other folders will be displayed.

Step 5. Double-click on Content

Step 6. Double-click on Shared Support

Step 7. Double-click Outlook Profile Manager

Step 8. Click + Create New Profile

Step 9. Name the profile
Enter a name for the new profile, and then click OK. This is usually your first and last name.

Step 10. Select the profile
After creating your new profile, click once to select it.

Step 11. Set the default profile
Click Set Default Profile and select Set Default. Now that you have a new profile outlook will be blank. You will need to link your account to this profile to be able to use it.

Step 12. Open Outlook
Launch Outlook, then click the Tools menu. The button is at the top of the screen.

Step 13. Click Accounts

Step 14. Configure your account
Add your email account. The necessary steps will vary depending on your email provider. To be sure to configure it correctly, ask your access provider for your login details.
- After creating your account, click on Always allow when prompted to synchronize your messages and calendar with the server.