「改札を出る」は
exiting the ticket gate
going out of the ticket gate
と言います。
「改札」ticket gate
「出る」exit または go out
I saw a friend of mine as he was exiting one of the ticket gates at Tokyo Station the other night.
「この前の夜、友人が東京駅の改札を出て行くのを見かけた。」
I passed by an old friend as I was going out of the ticket gate at the train station last night.
「昨夜駅の改札を出て行く時に、古い友人とすれ違った。」
ちなみに「改札を入る」と言うなら
entering the ticket gate
going in the ticket gate
のように言えます。
ご参考まで!