(to) “Get (one’s) Act Together”
This is an Idiomatic Verb Phrase which comes from the world of the performing arts: Ballet, Theatre, Comedy, etc.. The word, “Act” in this phrase is referring specifically to one’s performance. The Separable Phrasal-Verb, (to) “Get (something) Together”, is in-reference-to making that performance perfected and “in sync” with others involved in the performance.
(I Promise, No Click-Bait… Only Authentic English, and quite possibly a bit of inspiration)