Get Swipe Left in Mail To Show 'Delete' Instead of 'Archive'

Solution 1:

1. Go to Settings → Mail, Contacts, Calendars.

2. Select the Gmail account in question.

3. Select Account → Advanced.

4. In the second section called "Move Discarded messages into" change Archive Mailbox to Deleted Mailbox.

   The messages will then be deleted instead of archived.

Apple KB Article: Archive your Gmail messages

Solution 2:

While searching for a solution I accidentally noticed that if you set the default "Swipe Right" to "Archive" it will show this message below: "Accounts that include Archive as a default action for swiping left will offer Trash for swiping right".

I checked and now I get the Trash option as well! (even though the message doesn't make sense, we are setting the Swipe Right and not the Swipe Left as Archive).