Hi Gary,
The Forward Changes O.P. are not a figure in Tango. You may have been viewing them in either American style Waltz or Foxtrot.
Waltz:
https://www.ballroomdancers.com/Dances/info.asp?sid=117Foxtrot:
https://www.ballroomdancers.com/Dances/info.asp?sid=99Regards,
Jonathan Atkinson