Hi Shaoxiong Jie,
Thank you for posting to the community, I see that you are having issues in setting up in outlook, for me to better assist you, can I know if you are using a work or school account and in what platform Web app or Desktop app? Organizations sometimes disable IMAP, POP, or forwarding for security, so check with your IT team about that. Also, ensure you have the right permission to make those changes.
To check if the settings are reflecting on your Outlook App, you can initially try to sign in to outlook web app via https://outlook.office.com then login using your work or school account.
Also make sure you have the updated outlook version, to check this you can go to File then Office Account then Update Options then after that click Update Now in Outlook Desktop app.
Try using a different browser or clearing your cache, as glitches can impede saving changes. to clear cache just go to the settings of the browser then find Privacy & Security after that find Cookies and Site Data then choose a time range as All time then click Clear Data after that reload the browser.
Let me know if you find this helpful, you can just click accept answer and comment if your issue has been resolved or not.
Thanks,
Chard