The Google Mail App does not have the ability to change your passphrase manually in Settings. So when you change your Directory ID passphrase, you will need to go into the app and delete the old account and then load it back in using the new passphrase. You will not need to download the app itself again.

1. When you change your Directory ID passphrase, after a few minutes the Google Mail App on either your iPad or iPhone will return a blank screen. Tap the Manage Accounts button.
2. The Accounts window will open. Tap Edit.
   NOTE: If you do not see your current account listed at this point skip to step 6.
3. The Edit window will open, tap the Remove button.
   
4. You will be asked to confirm this action. Tap Remove.
   
5. The Accounts window will open. Tap Add account.
6. At the Sign In window, enter your full email address if this is a university account (e.g., DirectoyID@umd.edu). Tap Next.
7. The next window will have you log in using your university Directory ID and passphrase. Tap Login.
8. Your email will load into the app. This may take a few minutes depending on how much email you have.