I just changed a password and let 1Password save the new password. After saving, I discovered that the site had an error and did not in fact update my password, so I had to go revert the item in 1Password. It seems the only way to do that is, when viewing (not editing) the item, use View Password History to copy the password, then edit it and manually paste the old password into the password field.
It would be nice if there was actually a way to just say "revert to this password". "View Password History" should be visible in the Edit interface, and it should have an extra option to reset back to the last password (but probably shouldn't offer to reset to any older password). This option should of course require confirmation.
1Password Version: 7.2.1
Extension Version: Not Provided
OS Version: macOS 10.14 (18A391)
Sync Type: Not Provided