also hier der Auszug von der Bittrex Support Seite:
Remove/Disable Two-Factor

In order to have two-factor removed you will need to enter a support ticket from your valid email address. We will not be able to help you remove the two-factor unless your ticket is submitted from your Bittrex account email.  Once we receive your email we will reply with further instructions for removal.

Also kommst du ohne Support-Mail nicht weiter.