When you accidentally swipe left or right on an email in your Gmail inbox it goes to one of two places: Archives or Trash. You can locate the moved email by tapping the 3 lines in the upper left hand corner, then tap either All mail to see archived mail or tap Trash to see deleted mail.
To cover an email you moved, tap the email then tap the 3 dots in the upper right hand corner. Select "Move to Inbox."
You can also Undo the swipe action by tapping the Undo option at the bottom. This option only appears a few seconds after you move the email.
To change the action performed when swiping on an email tap the 3 lines in the upper left hand corner, scroll down and tap settings. Select the email you want to edit if you have multiple emails assigned to your Gmail app. Then tap "When moving messages, I prefer to..." You can now select Archive or Move to Trash.
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There doesn't seem to be a way to disable swipe gestures in Gmail. Let us know in the comments below if you know how.