milliepops
Wears headscarf aggressively
Haha! Poor Kira, has she got a reputation?
If he was good in the warm up then probably more about the change of environment than anything else? Sounds familiar, and in which case, as everyone else has said the best thing you can do is get plenty of match practice. I have found that arena hire anywhere and everywhere has really helped Kira because 5 mins to welly round a dressage test isn't long enough to get them over the demons of the new space. And then as the training at home develops, you can insist on better quality work as well.
I also try to get K really on the aids as we go round the arena before the bell, this seems to be more effective than letting her look too much because things look different from the inside of the white boards anyway
so she has to be reminded to prioritise me rather than worrying about each new grain of sand. So I have a little canter, ride some halts, whatever it takes to get her concentration again. Whatever we've done in the warm up is almost irrelevant by the time we've moved to the test arena so that is a critical minute or 2 IME 
and also he neighs even if we go to a RC lesson on our own. One of the livery horses at the venue did reply to him though on this occasion, which was annoying for me 