To move a message to another account:

  1. Select one or multiple messages from the message list
  2. Tap the Move to button in the action bar
  3. Go to Other folders & accounts
  4. From the drop-down, select the designated account
  5. Then select a folder

Please note that the feature is currently available only in the Message List (i.e. any account folder). It is not available in Message View (when an email is opened) or in the Smart Folder.