Call AC and give them the actual AC flight number that is equivalent to BD4860, your name and date of travel.

AC should be able find another PNR for you which lists you as being booked under the equivalent AC flight number as opposed to BD4860 (this may be referred to as the "operating PNR").

In this PNR, the actual AC booking class will be listed.

Also, if you want to do seat selection, it should be done in this PNR, and not the one showing the flight number under the BD code.