Meaning of “settle down” - Learner’s Dictionary

settle down

phrasal verb with settle uk us /ˈsetl/ verb
STAY

to start living in a place where you intend to stay for a long time, usually with a partner:

Do you think he'll ever settle down and have a family?
FEEL HAPPY

B2 to start to feel happy and confident with a new situation:

Has she settled down in her new job?

(Definition of “settle down” from the Cambridge Learner’s Dictionary © Cambridge University Press)