This is me speculating again, Bertholdt is still not found, as Armin stated in chapter 74 and 75, yet i believe he is still inside the walls as they yet havent searched inside (Duh, 15 meter Armored titan) so i believe he is still in the wall waiting for one of the other. Either he saves Reiner from Eren, squad Hange and Squad Levi *without Levi* or kills the horses if the smaller 3-7 meter classes fail the attack on the horses, possibly killed by the survey corps members thats keeping and eye out for the horses.
My second theory is that Bertholdt is inside the barrels the that the Quadrupedal Titan has on its back. The reason i think that is one of the barrels has holes that resembles the peek holes that Bertholdt was using. its also likely in my opinion as the Quadrupedal Titan is hiding behind the Beast titan most likely as a failsafe if the Beast titan is about to get defeated.