to get a grip (to control one’s emotions)

E.g. 1:

A: I feel so upset and angry! I don’t know what to do!

B: Get a grip! Your problem isn’t that bad!

E.g. 2:

A: Kelly is still upset about losing her job.

B: I know. She really needs to get a grip. She will never find another job if she is so upset all the time.