Despite being a generally superior Instagram client to most Instagram apps – including the official clients – 6tag for Instagram has always lacked the ability to log in via Facebook.
While on the way to making a universal app, Rudy Huyn had updated 6tag for Windows Phone 8.1 devices with the ability to login via Facebook.
If you can’t remember your Instagram user name and password, you can just use the integrated Facebook login log you into the account. Obviously this will only work, provided your Instagram and Facebook accounts are linked.
Download 6tag for Windows Phone here.