collect (oneself)

To compose oneself so that one's actions are not dictated by one's emotions. I know you're angry, so you need to collect yourself before you go in there and say something you'll regret to your boss. Take a moment to collect yourself, then tell us how the accident happened. I needed to collect myself so I could explain my side of the story, but I just couldn't stop crying.

collect yourself/your thoughts

1 try to control your emotions and become calm: I’m fine — I just need a minute to collect myself.
2 prepare yourself mentally for something: She paused to collect her thoughts before entering the interview room.