To determine or specify the truth: Let me set you straight on that allegation/ I've come to set the whole thing straight(1849+)
The Dictionary of American Slang, Fourth Edition by Barbara Ann Kipfer, PhD. and Robert L. Chapman, Ph.D. Copyright (C) 2007 by HarperCollins Publishers. Cite This Source
Idioms and Phrases with set straight
Correct someone by providing accurate information; also, make an arrangement honest or fair. For example, Let me set you straight about Lisa; she's never actually worked for us, or To set matters straight I'll pay you back Monday. It is sometimes put as
set the record straight, meaning “correct an inaccurate account,” as in Just to set the record straight, we arrived at ten.
[ First half of 1900s