This wasn't exactly training - the crowds were gathered there to see the Changing of the Guard, which happens every day there at Buckingham Palace (as far as I know.)
Training rides for new soldiers/horses usually happen at night when there is less traffic and fewer spectators, not right in front of the crowds for the Changing of the Guard.
Drill baby drill. Can't seem to find out much about it and never seen one used before. Guess it is simply for a cover for training.
On the other side of the flag cover is the ER II crest. https://files.catbox.moe/d4wi3z.png
This wasn't exactly training - the crowds were gathered there to see the Changing of the Guard, which happens every day there at Buckingham Palace (as far as I know.)
Training rides for new soldiers/horses usually happen at night when there is less traffic and fewer spectators, not right in front of the crowds for the Changing of the Guard.