To ~ something means to control it.
His administration’s economic policy would focus on reining in inflation...
Mary spoiled both her children, then tried too late to rein them in.
PHRASAL VERB: V P n (not pron), V n P
REIN IN
Meaning of REIN IN in English
Collins COBUILD. Толковый словарь английского языка для изучающих язык Коллинз COBUILD (международная база данных языков Бирмингемского университета) . 2012