Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
Hello. Priyatosh Arya
Welcome to the Microsoft Community!
We understand that you seem to be unable to open the OneNote app.
In order to help you better, please share with us a screenshot of the specific error reported.
Until then, we suggest you try the following steps:
- Restart your computer: sometimes restarting your computer can resolve a temporary software glitch.
- Repair Office:
First of all, please make sure that your Office applications have been completely exited. After that, right-click on the Start Menu icon and select Apps and Features or Installed Apps from the pop-up menu. Find Office in the list of applications, click on the menu of the corresponding item and select Modify.
Then, follow the guidelines in the Repair window.
If your OneNote is still not back to normal after trying to fix it, then you can try uninstalling and reinstalling Office completely.
For detailed steps on repairing Office and uninstalling and reinstalling Office, you can learn all about it in this article:
Repair an Office application - Microsoft Support.
We look forward to hearing from you so that we can help you better.
Best regards
InaX-MSFT | Microsoft Community Support Specialist