。。
Calm down. I'll be there in a sec.
Literal
Calm-down-[imperative] [emphasis-よ]. Right there [to-に] go [because-から].
落ち着けよ is the abrupt imperative of 落ち着く ('calm down') with sentence-final よ for emphasis. The second clause uses から in its 'because' sense but placed sentence-finally — that's characteristic casual spoken Japanese: 'I'm going right there, so [calm down].' Compact, punchy, reassuring.