1) Log into your MIT O365 email via outlook.office.com in your favorite browser.
2) Click on the sprocket icon at the top right corner on your browser window which is for your Microsoft 365 Email Settings.
3) Go to "Account" in the left Nav and select on Automatic replies in the center nav column.
4) Go ahead and edit the duration and contents of your automatic replies and remember to save them when you're done.