break somebody in

Từ điển Oxford Advanced Learner 8th

ˌbreak sb/sth ˈin derived
1. to train sb/sth in sth new that they must do
•to break in new recruits
•The young horse was not yet broken in (= trained to carry a rider).
2. to wear sth, especially new shoes, until they become comfortable
Main entry: ↑break_derived