Hacer changuitos literally means "to make little monkeys". It has nothing to do with monkeys. Hacer changuitos is a colorful way to say "to cross one's fingers". Like in English, it expresses one's desire for something to happen. It's an appeal to good luck.
Fátima: Neta que si alguien se merece esa chamba, eres tú.
Lourdes: ¡Haz changuitos!
Fátima: Por cierto, ¿el bikini es a huevo o es opcional?
Fatima: Honestly, if anybody deserves that job, that's you.
Luordes: Cross your fingers!
Fátima: By the way, is the bikini part of the job requirement or is it optional?